Many activities in Greece can be kid friendly, as long as you make some minor adjustments. The acropolis is a great place to visit but it can get a bit tiring for young kids who don't like being in the sun or walking up a lot of stairs. My first recommendation is to go very early in the morning, or late afternoon when there is not a lot of sun. Make sure the little ones are wearing hats and sunscreen and they are very hydrated. I suggest that you don't spend too much time at the top of the acropolis, but rather take a stroll through the museum and have a snack at the Café that overlooks the Acropolis. As always, you can make the experience more fun by getting some goodies at the gift shop.
If you’re interested in going to museums this summer when you’re visiting Athens, I highly recommend that you bring your student ID if you’re from Europe. All of the museums in Athens provide a lower fee for students and university.
I've seen so many people rent cars and drive all the way down to Porto Cheli from the Athens airport. While this is a great option if you prefer to drive, many people overlook taking a boat because it takes just a little bit longer. The reality is that taking a boat is much cheaper, and you also can be a lot more comfortable since you're able to walk around the deck, get snacks and coffee, and use the bathroom. Personally, I love taking the boat, because I also like to visit Hydra and Spetses when I am there and it's much easier to take boats to both of those islands as well.