It's so easy to learn, and there are plenty of activities (even simple "playing outside") where learning can happen. As a parent, all you need to do is encourage it. And also balance - it's completely normal to veg out and play video games as well - but only to end a day of exercising the body and the mind.
My point is not that learning is bad, it's that excessive and forceful directed learning is bad. Summer should not be the time you use to try and force more learning on your child, it should be the time when you let them learn the most important type of learning in life... self learning. Play is just that, the beginning of self learning.
Not to mention it's important for kids to actually have fun... Sure every kid is different and learn in different ways, however it's implicitly true that every kid will be happier and the learning will be more natural if it's through their own inquisitive nature and not because some horrible strict parent says you must be good at school or your'e in trouble.
Kids need time to be kids, and when they want help understanding something or are interested in something, that's what you are there for. Of course the same goes for not letting them veg out on modern technology, letting them have fun doesn't mean be a shitty parent at the other end of the spectrum.