hi! children and dogs should not be able to get into each others face. children are not dominant in a dogs eyes until their about 14 years old. your puppy warned the baby that he didn't like the situation. because the baby can't read the bodylanguage of the pup and there fore didn't leave the puppy acted the only way he knew how. a correction. dogs give eachother such a correction in nature. that the baby yelled is also a nasty sound for your puppy. your puppy has had a bad experience with children. don't let the child near your puupy. you need to protect your pup from the child aswell as the child for the pup. you should introduce your pup on a positive manner by giving him a treat when the child is near. don't let the child go to the pup but wait until the pup goes to the child. then praise him. your puppy acts normal and it's up to you to guide the association with children. never scold the pup when he acts like this this will enhance the behavior! he only acts like this because he can't go away.......
very normal behavior!