Having small kids around small pets that can be hurt easily can be tricky, but it can be done with a lot of supervision. My hubby (Ken) hold our grandson (Logan on his lap and lets him put him put just the very tips of his fingers into the cage to let Bandit sniff and lick him. We are very careful not to let Logan get his whole hand close enough so that he can grab one of the animals and hurt them.
Logan is always supervised when he puts his fingers anywhere near the cage where the rats are. Babies don't realize that they can hurt an animal if they squeeze too hard so that means we don't let him near any of the rats without good supervision.
Ken usually keeps Logan just out of reach so he can still see the rats but can't touch them.
When introducing a rat for the first time, there should be two people there. One to hold the child and make sure he can't grab the rat and one to hold the rat and make sure the rat can't run away or crawl on the child and scratch them. We let Bandit sniff logan and then logan petted him for a few seconds.
As you can see we made sure someone had a good hold on logans hand and wasn't able to to do anything but reach Bandit with the tips of his fingers. Bandit is one of my most friendly rats so we knew he wouldn't bite, nibble or scratch. He's a very laid back little rat and things went very well in this meeting.
It can be hard to have small fragile pets around children but with proper supervision, it can be done. I had hamsters, gerbils, rats and frogs around my daughter from the time she was 7 years old.