Some posters seem to be suggesting that puppies should not be on short leashes oniblic verges/pavements just in case errant children run up to them and are, gasp and pearl clutch, licked or jumped on.
That is exactly what we're saying.
Kids are impulsive. Puppies are very enticing and tempting to run up to. She is at a school gate where there will be -shock and awe- lots of children.
Puppies/dogs are also impulsive. A bunch of children running up to them is very stimulating almost to the point of over stimulating them. An untrained dog will get wound up, excited, and unable to calm down on command as the OP has likely noticed.
Right now the dog is small. When it is big, it can hurt the children.
Train the puppy, take it to obedience school, bring treats on the run to reinforce good, calm behavior. But don't bring an untrained one down. It could get over excited and bite or snap if kids are getting in it's face. With a crowd of children it's hard to control that.
Even good dogs will snap under stress. They are animals, they are not even particularly intelligent animals. A child in their face may seem playful to a human, but it can be threatening or aggressive to a dog. They aren't intelligent enough to understand the difference between a child innocently poking their face in theirs and another dog doing it aggressively (and if you're letting your dog get up in your small child's face, you're playing with fire). Even the most laid back dog will act on instinct and forget training if they are over stimulated or stressed unless they are specifically trained to handle stress (work dogs), and even then the trainers will only pick out certain puppies to train. Not every animal can be taught to be calm next to stimuli.
I'm not saying OP's dog will get aggressive, in fact, I doubt he will. Most excited dogs don't if they're socialized correctly. However, all that stimulation is stressful to a dog, he could forget they are children and not other puppies and play bite. You don't want that.
This is a terrible environment to teach a dog in. She is reacting by pulling the dog away, which will cause them to get more excited and want to jump more. The dog needs to learn in a calm environment before being taken into what will become adhd doggy crack land with all the loud boisterous children.