Firstly, this is why you have FOOTPRINTS of small babies
From my experience of trying to do it with a 6m old and a 23m old the other xmas...
First get the 23m old to do his, wash him and put him in front of a disney dvd
Shout for dp.
Dp holds baby. Mum paints paint on baby's hand, puts paintbrush down, pics up the canvas board thing. Dad takes baby's arm and sort of pulls the skin back on the back of the hand/wrist area. Errrr, it may sound cruel but it opens the fingers.
Now the crucial bit.
DO NOT try to lower baby's hand on to canvas.
Immediately the fingers are open, mum whacks the canvas up to the open hand and takes it away straight away so less chance of smudges.
Wash baby, hand, table, selves etc.
Repeat with other hand.
Then because we were completely stupid we repeated all that with another colour and kept going for ages till we had enough farking handprint canvasses for all grandparents and great grandparents.
THe next year we just bought them all pressies from shops.
I bought non toxic paint wipes off ebay to take DS's hand / footprints but didn't get round to it til he was 14 weeks, even then it was hard to uncurl his hands! The wipes are great though, no need for brushes and all that malarky. I also took the prints on paper then cut them out to put in his baby book later so I didn't get paint all over the baby book
I just used one of those sets where you get a good sized canvas with a set of acrylic paints. We were so exhausted after doing the ones for the gps and ggps (damn the il ggps for all getting divorced and remarrying ) that we never did the biggest one for ourselves. Thanks for posting this thread I think we will get that out of the cupboard and get it painted this weekend. Ds2 is 2.5 now so hopefully I will only need to supervise - no manhandling required!