"For a four year old you call the parents and ask what he is into, or run your idea past them."
Heck, for a four-year-old you grab a box of sidewalk chalk, or a playground ball. It's a four-year-old. Do the parents really think it's that tough to figure out what a four-year-old kid would like? It's not like they're into hobbies or music at that age. A registry announcement for an adult would be a faux pas. Why would any parent think it's different for a child?