Summer is too long. It is hard to keep children at home especially when both parents are working. They would resort to all PC games on the internet. What's more frightening is that they might accidentally click on to an adult website and you might not be aware sometimes that they have been sneaking on your back, clicking on something that should not be. Two months is long enough to keep them safely and productively situated at home. With the gaming gadgets, I don't think you could keep them away from those when they have nothing to do but stay home.
Outdoor activities would be great as their exercise but sometimes outdoor games may cause them so much harm. Not just with too much exposure from the heat of the sun but they might just get hit by the raging vehicles outside. There are safe fields that they can play, like in covered basketball courts. They can do all sorts of games in the premise but not all the time because it is meant for playing basketball, but at least they can be kept from too much warmth outside - and clearly, it is one great time consuming activity. Another is to enroll them in summer clinics like basketball, volleyball, Taekwondo and more, of course that would depend on your child's interests. They can also spend time doing paintball, some fields are covered which makes it safe from too much sun exposure especially mid day. Paintball is okay. It doesn't hurt that much for adolescent kids especially boys. They will enjoy so much time inside the paintball arena. You can leave for a while to do your important errands like shopping without thinking so much of the stubborn little one. Paintball will help them to be cooperative and will make them work as a team. The kid will be able to socialize a lot with different kinds of people. It is not just an exercise and not just about keeping him busy but there are a lot of benefits he will gain from paintballing. As a child he would learn to accept defeat. He would be very responsive to his team of players. And he will learn to socialize with others, aside from the physical benefit a child would gain.
If you want a more educationally - inclined summer school, I would suggest the Speech Power. It is not all about talking; it is talking the right words with the right pronunciations. And also how you carry yourself right, while doing your speech. There are also courses about Public Speaking. Also nowadays, there have been Math Clinics for children with deficiencies in the Math subject. There is also about Art and Creative Writing. Catechism for the kids and it's for free.
There are a lot of activities. And when you follow my suggestions, the entire summer will not be enough to accommodate them all. A lot can be done and so much can be learned so you better start planning your next summer.