What medium did you use for these? I did a similar project last year and no matter how hard I tried, I couldn't get my kids to effectively paint with tempera paint...meaning they painted very streaky!
We used tempera paint too for everything except black, which I just had them fill in with Sharpie markers. Streaking is always a problem - my kids are probably sick of hearing me say "LONG PAINT STROKES" every few minutes of a painting project!!