When my first son was a toddler I had a difficult time finding good protection for those afternoons of painting or playing with stamps. All the aprons that were properly waterproof (and paint proof) were normally too big (designed for preschoolers or older) and quite rigid. This was until I decided to try the Babybjorn Eat and Play Smock. I think it was meant to be a bib but it works perfectly for a painting coverall, and it’s the right size — I would say it’s perfect from 1 ’til at least 3 years old. It’s soft, waterproof  and can be machine washed when it gets too dirty for a simple wipe.
Plus, as with all the babybjorn products, it is super-safe and this smock has obtained the Oeko-Tex Standard 100 certification that ensures the textiles do not contain concentrations of substances that could be hazardous to human health.
Ours is still in perfect conditions and it has already been handed down to my little daughter, not that she can paint yet!
Also available through Amazon (US  or UK).

-Michela