Aggressive behavior towards my toddlers

I have a 3 and a 6 year old.Both girls. when I take walks I make sure that the 6 and the 3 year old hold the leash,I also make sure the dog knows they are walking him. I have a pinch on him and my 6 year old knows the perfect time to correct and does it right. So the dog knows that he is to listen to them and they are above him in the"pack". I feed the kids in front of him and sometimes I have the older one make him his dinner.She will also tell him to sit and wait and she will not feed him till he does this. Does your 3 year old like dogs? Is she scared of her?Do you do any training with her,if so make it a game with the 3 year old. Make the dog sit and give treats with the 3 year old next to you,the next time make her sit and have the 3 year old treat,then if your daughter has a good vocabulary have her give the command to sit and then treat.You have to let her know that your kids are in the pack and higher then she is in it,If you yell and correct though she will get negative vibes about when the kids are around so be careful.

Very small children can be very irritating and annoying to a dog/puppy. Were the children too "clingly" initially with the dog in their excitement of a new dog , not giving her space? Perhaps hugging and hanging and maybe even pulling hair or tail?

The little ones can pester, chase, take away the dog's toys, tease, etc (not saying that this happened - but would be typical of children that age) and make it very difficult for the dog to avoid them. The dog probably gave many warning cues prior to the growling but perhaps were missed by you not being familiar with this particular dog. Did the dog move away , pull away from their hugs, avoid eye contact?, etc. jump on you as if to say help me deal with them?....Avoidance is usually the first line of defense and then if cues are missed it escalates from there.
When folks buy puppies here I always make sure that if they have small children they understand that they must "protect" the puppy from the kids. I am not saying the children have been intentionally bad to the dog but they must respect the dog's space (ie not crawling or bothering in the crate or food or toys) The movements , sounds and smells of children can all be intimidating and overwhelming especially with a dog of unknown background.

Yes immediately get help from a trainer the warning signs are all present for a bad situation to develop. Never leave this dog unattended with the children not even for a second.

How do you react when she barks or growls at the children? I know what I would do but am curious what you have done.

A good book I recommend is "Raising Puppies and Kids Together" A Parent's Guide by Pia Silvani and Lynn Eckhardt

Please get help soon for this situation and let us know how she does with training.

Apparently this dog has shown a tendency to be a bit of a dominant bully with other dogs. It's not surprising that she would show this behaviour to kids that she looks upon as little more than inferior pack members. This could be a tough situation because after owning the dog for only 6 months or so one could question exactly what is the heirarchy of the pack in the dog's mind.
I know a lot of folks want to use only positive methods but to me there are a few instances where "shock and awe" methods are called for and aggression towards children are at the top of the list.
I disagree with the idea that there should be no yelling or correction when aggressive behaviour occurs. I would leave absolutely no doubt in her mind that the BOSS' tail ain't waggin' and if the Boss ain't happy, she ain't happy. Nobody really knows what goes on in dog's mind but I don't see why she would associate the correction with the kids when it only came from the boss after she exhibited aggressive behaviour towards the kids.
Once the smoke and radiation have cleared then I would begin the "kill 'em with kindness" campaign from the kids. High value treats from them. "Hmmmm, these rugrats aren't so bad after all."

It would be nice if you could borrow somebody elses kids and see how she reacts to them without anybody else around. (just kidding)
She may just be the jealous/protective type and if she didn't see them as a threat to your undivided attention and affection would likely ignore them or more likely just try to herd them around.

If this were a pup I'd feel a lot more confident in a good outcome but at 4.5 years she's likely pretty well set in her ways, especially attitude wise. I wish you well in it, but I don't know how I could ever be comfortable unless I saw a profound improvement in her attitude.

Chris' comment about "Shock and Awe' is exactly what would have happened here, that dog would have ABSOLUTELY no doubt in it's mind ANY aggressive behaviour with kids would be dealt with severely and immediately. That is why I was curious as to what the OP did when this aggression occurred. I'm sure as I mentioned earlier many warning signs were given but not dealt with as they were not recognized or they "hoped" it would get better.
The OP has never had to deal with this type of behaviour as she mentioned regarding her other 2 females in the past. If you have never HAD to harshly correct your dog you may not really know "how" to do it OR "how" much is really necessary to get your point across. The other issue is the OP knows this dog is aggressive to other animals and may have some fear/hesitation/doubt about how this animal will deal with a harsh correction. Not knowing if this dog could come right back at them.
One thing that bothered me about the OP is that they "chose" to rehome the male while acknowledging that the female was clearly the problem! Maybe in their desire to have another female they were blinded by emotion?
I would give little time for improvement as the safety of your children is utmost and after that time rehome the dog if necessary in a home without children. Four and half years of age IS going to be difficult to change and I probably would never feel comfortable with this dog in the house with my kids.

I have 3 boys, ages 5, 6 and 8.

I can tell you without a doubt...if my girl (who I love to pieces and would do anything for) showed ANY aggression toward my children..I would be IN HER FACE in a heart beat.

We'd have a 'Come to Jesus' meeting on the spot.

I am not of the old school mentality. I don't generally use any negative training methods. I stick with positive reinforcement, socialization, and all that jazz.

But there are some things that are not tolerated, and the 'wait and see' approach isn't even an option.

Growling and barking at the children of the house is one of those things.

My opinion/input...when the children are there (which at their ages is likely all the time) the dog is on a lead attached to you.

NILIF sets in immediately. The dog gets nothing without doing something for it. All special priviledges are GONE. No up on furniture, etc. The children don't sit on the floor.

The dog watches the children eat first, get attention first, walk through doors, into rooms, up stairs, etc first.

I would also put the dog in a sit at feeding time and let her watch the children put the food bowl down. They should be seen as controllers of everything good in her life as well. If they can give the sit and release commands themselves it would be even better.

The second any negative reaction to the children starts, correct. If you are unsure of how the dog will take a correction (especially if it needs to be harsh), I would seriously consider a muzzle.

This is something that needs fixed ASAP. If you don't feel it's something you can tackle on your own...find a trainer/behaviorist to work with.

Also, I would not consider rehoming her. IMO it's too much of a liability. Unless you could find a professional trainer, someone with no kids and experience with a dog like this to take her...it's a crap shoot. You would need to screen very thoroughly.