One thing that is perfect to do outside is art. The children can make as much mess as they want because the teacher can just wash it away. Children love to get messy and this is a perfect way to get messy without having to take a lot of time to clean up.
At daycare centers or preschools if water play is offered or even if you are at home with your own children. You can have the children wear bathing suits while painting and then run through the sprinklers which will clean off the paint and it is fun for the children.
Outside the children have more room to run around and help get that exercise that is needed every day.
Another advantage to doing things outside is that the art projects will dry quicker for the children to take home for their families.