Your Yorkie is probably nervous of them..and rightly so! children can accidentally injure a small dog..and i think they can sense this so are naturally wary of children...is there a reason your dog is so nervous around children? My sisters 4 month old King Charles spaniel has become aggressive around her two younger children (3 and 8 years) because they continuously annoy the poor dog..waking it when asleep and constantly picking the poor thing up so it was growl and snap..it is the only way the poor animal can tell them to 'BACK OFF'!