Yep, I agree, not finger paints.
Poster paints - water soluable, bit wishy washy colours, will fade with time, cheap to buy
acrylic paints - water soluable (if you get it when wet), bright lovely colours, more pricey, will last forever.
My vote - acrylics in old clothes that you don't mind chucking out. And, lots of old shower curtains/paper on the floor, and take about elevnty billion prints and choose the best two.
good luck!