We sign every birthday card (will do Christmas cards) with his footprint in the card. We use one where no ink goes on his skin and it prints onto the card x like this - Nabance Baby Handprint and Footprint Kit, 3 Baby Inkless Print Pads, 6 Imprint Cards, Baby Footprint Kit, Safe Non-Toxic for Feet and Hands, Family Keepsake - Black https://amzn.eu/d/8fTNZGH
We've used the washable crayola ones and just washed off straight away and been very thorough with the clean off 😊
You can look up non toxic paint for babies there's also washable paints I think by crayola just make sure to be vigilant or I've seem like paint sticks as well that could be good