I didn't want to change out my ceiling fan so I bought skateboard ceiling fan blades when we decorated our son's bedroom in a skateboard theme. Just so you know you can buy a new 42 inch skateboard ceiling fan for the same price as the individual, fan blades but considering that you will either have to have spent time or pay somebody with electrical skills to come and mount it on the ceiling buying the replacement blades might be cheap in comparison.You can get them in all kinds of cute themes that perfect for kids' bedrooms like skateboarding and lots of other sports.
We bought five skateboard ceiling fan blades for our 52" ceiling fan that were 21" long and the kit stated that they would that fit most 52" ceiling fans. The blades come drilled with holes for mounting but we had to drill some more to make the holes line up on one or two.
And another great thing about them is that the decorative skateboard fan blades are reversible with a solid finish on the other side so that when your child outgrows a particular theme, you can simply turn them over without having to paint or replace them. We expect our children's ceiling fans to last a long time so this is an important feature for us!