Such a good idea as a gift for grandparents. Put a phrase or message in vinyl letters on a clean canvas. Have your child paint a picture on top, then peel the vinyl letters off to reveal the message underneath.
The Eiffel Tower, Minecraft style. i must admire how long a) it took whoever created this to build it but more importantly b) How long it took the ORIGINAL architect (Gustave Eiffel) to get the real thing built (around 10 years if i remember correctly.