You could build a plain desk for your child but you could also build this house frame desk for bonus points. Follow the free step-by-step plans at the link.
This house play table which features an angled desktop is perfect for little ones to get creative. Follow the free woodworking plans at the link.
This fold down desk is perfect for a childs room where space is usually at a premium. It is easy to build and install using the free building plans at the link.
Build this beautiful kids desk with storage using these free woodworking instructions. You can modify the height of the desk if you are building it for an older (bigger) kid.
Build a house shaped childrens desk perfect for crafts and coloring. Free plans at the link.