Is it ok to wear different colors in group portrait?

I want to get pictures taken for my mother-in-law with all her grandkids. There are only five of them, two girls, three boys ages 5, 5, 4, 1, and 6 months. I was thinking of having them each wear a different color shirt with brown paints. The colors I am thinking are dark orange, green, and red, and doll colors of yellow, and pink. We will be taking the pictures outside and I think it will ether be really cutie or really awful. If someone could tell me if it will work, how to make it work, or if there is something I should do better that would be great.