I found a great way to get my 5 year-old involved. She loves to paint. I hate to assemble kits of brick buildings without the mortar being painted. Instead of using acrylic, I pulled out the good ol' Crayola tempera paint and let her coat the building sides. After it dried, she took a wooden clothespin and ran it over the surface, leaving perfect mortar lines in the brick siding. Awesome!