If you are a family that does not want to take off lessons for the summer, consider at least 2 or 3 weeks off for your student. It will do everyone good! Minds need rest.
If you are a family that wants to take off lessons for the entire summer, certainly consider scheduling at least one or two lessons each month, or attending any music/piano camps that your studio might offer. This will keep a student at least at the level they were at the end of the last semester. You don't want a student to lose any hard-earned progress, which is inevitable if they do not take any lessons for that length of time.
If you are a teacher who freaks out about students not taking lessons, make sure parents know that you are willing to do less than weekly lessons, or offer camps in various subjects. I really do not think that it is possible or decent to demand parents to pay for and bring their child to lessons during the summer, so be creative in ways to get a student in for a lesson. Just don't give lessons for free; that is a slippery slope! Also, just enjoy some time off. Take a break!