What is a good way for small 11 year olds to make money?

You can try baking some cakes, muffins; etc and sell them at a market.

Make lemonade.

Collect pinecones and sell them for about $5 a bag

Garage sale, Your family and friends might have some things that they don't want.

You could do chores for the elderly like mowing the lawns, doing some weeding or gardening.

Walking dogs or pet-sitting.