There's a reason why parents don't look forward to the summer nearly as much as teachers do. Summertime with two children at home can get long and boring. And long and boring makes for a lot of grumpiness at best... and troublemaking at worst. Aside from the schedule I try to keep during the summer, I also try to plan various outings and projects to keep my children busy. The problem with that is it can get to be quite expensive if you are not careful. So, here is my advice to keep your children busy (and you sane and not bankrupt).
Go to the library. I love the library! And not just for checking out books. Local libraries often have story times and other activities geared to different age levels. I have taken my children to plays, presentations, and craft times at our local library. And those events are usually free.
Hit the park. Although here in Texas, you have to plan when you go around the heat of the day, parks are a great place to take the kids. You can take a picnic and just let them romp on the playground or find a park with hike and bike trails. Plus, this gets the kids outdoors, which I believe in strongly.
Go swimming. A wise friend of mine once said, "Cranky baby? Just add water." Most kids love to swim. Scope out your local pool, splash park, river, lake, or beach... and go often.
Arts and crafts. You are a teacher. I know you have tons of crafty things around your house. Gather the supplies together and challenge your children to create something.
Encourage the imagination. I don't know about your children, but my kids love to play with things that are not toys. Give my son a laundry basket, and he's occupied for hours. Cardboard tubes and boxes are more favorites. And my 13-year-old loves the duct tape!
Have a staycation. I am lucky to live in a very touristy city with tons of things to do, many of which are free or very inexpensive. If you live in such a city, check out the Convention and Visitors Bureau website. You may discover things about your area you never knew. And they often have great coupons and deals too. If there is not a CVB in your area, you can just Google search for things to do. My family personally loves daytrips too, so that can expand your options.
Sign up for Groupon (or other deal services). Groupon is great because you choose your area, and they send you local deals. This allows you to take advantage of all your area has to offer without spending and arm and leg. I have gotten great deals on ice cream, restaurants, and attractions.
Get a season pass. If you have a favorite local attraction, it is usually most economical to get a season pass. The pass often pays for itself in 2-3 visits so it can be very worth it. My family has a membership to our local zoo because we love to go often. Plus, the passes give us discounts on food and souvenirs.
So get out and get busy. It will make you and your kids happier this summer.