I have a mixed group ranging from 12 mos to 3 years. I have the toddler sized table and stools and do more advanced crafts with older kids while little ones free play, then do (often) a different craft with the younger ones, if they're remotely interested. The little ones will, of course, come and check out what we're doing, but will generally leave the materials alone once told a few times. If you're sitting right there, it shouldn't be an issue. You could, since the weather is lovely, do a messy craft that everyone can participate in outside. A bucket of water and some washcloths for an easy clean up and you're good to go! A fav here is to take a long piece from a roll of paint paper (maybe 6 feet or so) and bowls with different coloured paints. The kids (even the little guys) love to all contribute to the giant picture. Or they can walk in the paint, then walk on the paper. Or splatter painting with watery paint. Bubble bath or dishsoap in a water table or couple inches of water in a paddling pool is heaps of fun too! Treasure hunting in the sand box (draw treasures or faces on container lids and bury...or larger shells/painted rocks). These are really fun and the younger kids will participate once they see how fun it is. They're naturally curious about stuff and these are some of the more fun activities we do.