Rent a Room
Summer Day Camp/ Day Care
Remember before starting to check the laws of your country/ state to see if there are no legal restrictions.
Plan Summer Parties
Are you a stickler for details?
Then maybe planning summer parties is a prefect way for you earn extra money.
You can plan summer theme parties in which persons can pay to enter. Another way is that you can plan events in your home or back yard in which you can sell pastries, ice creams, jewellery, D.I.Y creations, etc.
Don't knock it until you have tried it. Just use your imagination to create some great ideas that can be turned into a business idea.