Hmm.. Grim is in his 5th month, and it still teething, so I thought yours would still be getting some molars in as well. I can tell you that my 2 year old Pug still chews on nylabones and steals Grim's antlers like she's still teething, and I know better.
Maybe he's just bored or an avid chewer then? All my shepherds have been 'mouthy' their whole lives. Something about the breed. So your pup is taking their food from the table? Right now, we still crate Grim at mealtimes so we can eat without having to watch him, but my previous shepherds weren't allowed to mill around the table at mealtimes. They had to go in the living room and lay down. Maybe start training him to a 'place' (bed, blanket, etc. on the floor) to go to when anyone's at the table. Our dogs growing up would literally make a quick exit from the kitchen when the table was being set. My dad was VERY strict about no dogs in the room while we were eating. My youngest used to have his food snatched, too. (He also thought he was a diva, and would 'wander off' with his food!) A sharp "NO!" and "go lay down" solved the problem with time and consistency. Your pup is entering a tough time. When it's about time to start corrections if they do something they 'know' is off limits, and finding creative ways to teach them what isn't OK...but doesn't really have a word to it. I'm about to enter that 'zone'...again...so I feel your pain.
I haven't heard of doing that with mouse traps, and I've cured every dog I've had of counter surfing. The issue, I think, is during puppy hood I wouldn't want anything that could cause them to become reactive. In my mind, I'm seeing a dog that stands and barks at your counters for X months-years because there's something 'scary' up there. The other issue would be if the mouse trap actually managed to get him. I had one 'trainer' tell me to put mouse traps in my cats' litter box (and keep the cats away) so when he stuck his head in, it would be the last time. It sounded like a BAD idea, so I didn't do it, and that was the last time I spoke with that 'trainer'. You know your dog. I know that Grim will exact revenge on whatever has surprised him or pissed him off. He'd be barking and biting at my counters forever if I did that. Right now the only time he puts his feet up on the counter is when I'm getting his canned food ready and I'm being too slow.
Right now, it's a teachable moment for the word 'off'. "Leave it" is also in the works. Possibly the 2 best commands, ever.
You can also work on "mine". This can be used to claim anything that the pup/dog isn't allowed to take or mess with. You can use food on the counter for this, too. I may have put too much together, but it went like this... dog jumps on counter... I have a plate or bowl with 'my' food on it. "NO. MINE. Leave it." If the dog gets off the counter and leaves the food, praise. Show him something that is his. "Hero's. Take it" Praise. Anything and everything on the counter is "yours". It's not a quick fix, but it DOES work. My dad went so far as to put his plate on the floor and our dog wouldn't go near it. Of course, he trained with a LOT of compulsion. It could have been trained differently, but that was then I guess. If you're not still tethering at this point, you may want to at least have him drag a lead so you can grab him before he helps himself to your kid's food. Kids and pups can be frustrating together, but they both grow up, and with training all the way around it will get better. I promise! Don't discount yourself as a trainer. We all have to learn, and the learning never stops. We all slack off from time to time. You and I have the same new goals... to get back on top of our pups and training/exercise. I haven't been doing too much for training because I didn't want to have to go back and undo what wasn't right (I plan to title Grim)....so I'm THRILLED that his classes will start early January!
They turn into little monsters when their mind isn't being challenged! For now, just try to keep all foods off the counters or pushed back. Then have your daily or twice daily training sessions for staying off the counters when there is something good there, and teach him what "mine" means. I think you'll be as happy with the results, without the possible complications.