I am not sure why you are so bothered. The dog is 10 months old. He is in the adolescent stage where he does not know whether he should be hiding behind you or protecting your property. He is a puppy and an adult, think of a 16 - 18 year old boy. He needs guidance.
The dog is a German Shepherd that has evolved into a sheep herder/livestock guardian, guard dog, police dog, service dog. You know this. You named him Sarge. He will be a formidable dog who will deter burglars. He looks great in his leather collar.
Only he doesn't know the difference between harmless neighbor with kids in tow, and big bad burglar-man. He needs guidance.
He is at home on his property, or yours, not sure if there is a difference in his mind, with his person, some dogs will be more protective of their domain than others.
What have you done in the way of socialization and training? Remember that babies walk and look and SMELL different than adult humans. If he has never encountered a baby or toddler before that can be your problem. A stroller might be another item he just hasn't encountered.
The thing is, up to this point, his puppy head was not concerned about the big bad world out there. But now, he is growing up, and things he has started to classify things as things he knows are fine, and things that need to be chased away. He needs guidance.
If you haven't taken him to classes, you need to get him out there and go. You need to be careful at this point, but you need to expose him to things safely. And it won't happen over night. Plan on him being a lot better in a year, but that is only if you make it your business to work through it.
RIP Arwen, CD RN CGC
RIP Whitney, RN CGC
Jenna, RN CGC & Babs, CD RA CGC HIC (not AKC)
Heidi, RA CGC & Tori, RN CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear