Remember what it was like when you were a kid in the summer time? Once that last school bell rang for the year, you ran outside and basically stayed out there until that same bell rang in September for the start of another school year. Our parents would send us outside for hours on end, and it was never a problem. If we got hot, we ran through the hose. If we got tired, we would sit under a tree with a book.
Considering the fact that children are spending an average of two hours less outdoors than they were just 20 years ago and the increase of childhood illnesses has increased, our parents may have been on to something. There is just something about that fresh air.
Being outside has many advantages for humans: it gets us out of the stale, recirculated air we breathe on a daily basis, the sun can give us a good dose of vitamin D, and it encourages exercise. All good things. Of course, when it is hot out and the sun is incredibly bright, you will need to find things to do that help keep your cool while staying out there. Plenty of sun block and drinking water will help.
If you have kids who prefer being indoors, try bringing a little bit of the indoors outside. Play board games on a blanket in the yard. Allow some video game time under an umbrella. Make being outdoors the norm and being indoors more of a treat. Give them a better appreciation of the outdoors by making it an enjoyable place to be. Plant a garden together or set up a water station using a few buckets and some bath toys. And while your kids are playing, grab yourself a book and join them out there! You could use some of that fresh air yourself.