First I gave them a good sanding
with medium sand paper to smooth out the wood and get rid of those little splinters. I paid special attention to the edges which were a little rough.
After they were sanded, I wiped them down with a damp cloth to get the saw dust off. Then I used a different color spray paint on each crate . The lighter colors needed two coats, but the green and blue needed extra to get a more even coverage. Let dry thoroughly between coats.