If the second-hand wood desk you find is too tall, shrink it to size by sawing off the legs. Measure the height of the desk, determine the right size for your child, then cut carefully to keep the legs even and stable. Save the cut sections to reattach later when the child needs a taller desk. A low wooden stool is an acceptable desk chair for an active younger child. When measuring chair and desk, be sure small feet comfortably touch the ground and the desk surface is a good height for scribbling and coloring.
A reproduction antique desk and matching chair can lend just the right touch to room of a little prince or princess. You can buy desks that look as if they were crafted during the reign of one of the French kings, and you can get them painted and gilded to order. You can find them at children's furniture boutiques and online; with a good eye and a bit of luck, you may stumble across one for a reasonable price at a consignment shop or yard sale. Unlike the actual antiques, these reproductions are very sturdy and can absorb boisterous kid energy.
Paint a simple map of the world on a wooden child's table, and paint the chair in solid colors picked up from the map. Use the nicely proportioned furniture as a desk until your child is big enough for a "real" desk. Find sturdy, well-made wooden furniture for kids at an unfinished furniture shop. Finishing the furniture yourself saves money and lets you custom design to match room décor. Turn the table into a desk with a plastic "inbox" to hold loose papers and a non-breakable souvenir cup for markers and safety scissors. The desk also works as a drafting table, tea table and game table.
Hunt for children's desks in consignment shops, flea markets and antique stores. Mid-20th century furniture was often brightly colored with simple modern lines that are very appealing to a child and easy to fit into the décor of a kid's room. If you find a desk with a good design but a boring industrial finish, paint it with auto body paint or metal paint in a bold primary color. Add a few whimsical touches -- a cartoon character mug to hold pencils, a painted sand pail used as a trash can, a desk lamp in a fantasy shape -- and homework will almost seem like fun.