Some people find the acids in their skin tarnish their jewelry, other people don't. But all sterling silver jewelry will tarnish with time and exposure to air. When she's not wearing her sterling silver children's jewelry, put it into a plastic zip-lock bag (you can purchase very tiny ones to hold one or two items of kids' jewelry, at "dollar stores." Squeeze the air out before you zip it closed.
This will help prevent tarnishing. But when her little silver children's earrings, bracelet or chain becomes tarnished, don't rush out and purchase expensive and toxic silver cleaners. Try this "green" method for cleaning her silver items.
Most people have baking soda in their cupboard. Line a small bowl with aluminium foil, shiny side up. Lay her chains, bracelets etc. on the aluminium foil (items must actually be touching the foil.) Sprinkle approximately one tablespoon of baking soda over the jewelry and pour boiling water over them.
At first it will bubble up. This is harmless and will stop within seconds. Leave to cool.
I have read that this method works in one and a half minutes but I tried this on some children's chains and it didn't make much difference. But I've since tried leaving it overnight and it did make the chains come up nice and shiny.
I've also read that you shouldn't use this method on marquesite jewelry or some gemstones, or pearls. so bear this in mind.
Many people store their baby bracelets once they're outgrown, as keepsakes, in tissue paper in a cardboard box but if they are first put into an airless plastic ziplock bag, they will tarnish much less over the years. When the time comes to give her, her baby jewelry back when she, in turn, has her first baby, you will be able to make them look brand new again, and she will be thrilled!