Most importantly you should make sure they are the correct size for your child. Check the material the galosh is made of to ensure it will hold up to the elements. The inside should be insulated to protect your childs feet from the water. I would recommend the golashes with the handles on top for easy on and off.
To get the child to wear them, a fun looking pair (alligator, lady bug) is helpful. Find some that are big enough and comfortable. They should be a rubber or rubber-like material and should be at least 12" in height. I like the ones that have loops on the sides. It makes them easier to be pulled on.
1. Make sure the galoshes fit over the child's shoes.
2. Make sure the galoshes fit well enough over their shoes to not slide and swing around their feet.