There are a ton of ways that an 11 year old can do to make money. It just depends if you're willing to work towards it. You can either have an allowance from your parents, or make a deal with them. Do chores, for an allowance. Work towards what you want.
My mom let go of the house lawn mower because it was kinda expensive. So she bought me a lawn mower so I could do it. In return, I got internet for me and my siblings at my new house now. Like bouchra said, you can sell of things if your parents are okay with it. Just be careful. You can also offer to do something for your neighbor. Like washing their car for them or mowing their lawn. There is a variety of choices. Just depends if you're willing to work for it.