Taking summer vacation is normal. But even if s/he can't play in tournaments, s/he should still play online and solve tactic problems by him/herself. To minimize the impact, s/he actually should double his/her efforts when s/he has time. Playing chess is time demanding, and being a good chess player is a commitment. One has to work hard to improve.
Summer in fact is a great time for chess study and chess training. There are less scholastic tournaments, but more large tournaments involving adults over summer. These are great practicing opportunities. There are also a lot of chess camps of all levels around the nation. No classes, no homework. Your child will have plenty of time to study and play chess, as much as s/he is willing to.