My son is nearly 13 and we have been to bali many times, and always always go to Legian beach no matter where we are staying, and look for guy straight outside the Melasti Beach Resort, he hires umbrellas, chairs etc. I always forget his name, but he is great, and will go out with your boys for a small fee, we give him between 50,000 and 150,000 RUP, depending on how long he is out with son. He is happy with whatever you can afford. Otherwise he'll stand on beach and watch and help if needed. He is a lovely man, and has a son who enters all the competitions he can in Indo. We are there jan 23, and will def be there again with him. We take him clothes etc for his family that son has grown out of, and he is always so glad. Such a lovely family. Good luck.