Start with washable paint! I have found these finger paints from Crayola work very well and wash out of clothes and off hands easily.

https://www.amazon.com/Crayola-First-Fingerpaint-Washable-Paint/dp/B0197UC222/ref=sr_1_2?ie=UTF8&qid=1512750743&sr=8-2&keywords=toddler+paint


Big brushes are easier for little hands to grip!

https://www.amazon.com/Melissa-Doug-Jumbo-Paint-Brushes/dp/B000M5J7W0/ref=sr_1_4?s=toys-and-games&ie=UTF8&qid=1512750973&sr=1-4&keywords=toddler+paint


An art smock with long sleeves is great and spill-proof paint cups will help contain the mess, a little!

https://www.amazon.com/Children-Waterproof-Painting-Pockets-Bassion/dp/B06X6H6H29/ref=sr_1_1?ie=UTF8&qid=1512751088&sr=8-1&keywords=long+sleeve+art+smock+for+kids

https://www.amazon.com/Melissa-Doug-Spill-Proof-Paint/dp/B000FAB7I4/ref=sr_1_1?s=arts-crafts&ie=UTF8&qid=1512750904&sr=1-1&keywords=toddler+paint

To contain legos and other small toys, I love play mat bags. They make cleaning up small toys quick and easy, plus they act as storage.

https://swoopbags.com

https://www.3sprouts.com/collections/play-mat-bag

The Lego Storage Brick makes it fun for kids to help out with clean up. The storage compartments even stack like legos!

https://www.toysrus.com/buy/tables-storage-accessories/lego-storage-brick-8-blue-40040617-18516846