I would highly recommend the Shangri La hotels (Al Waha or Al Bustan) with Children, if you are travelling to the Muscat area of Oman. They have some of the better beaches, although it is a little far from the city centre. You can use the facilities of both hotels. The kids club is amazing, based in a Sail Ship. (on land replica)
Ps. Do remember if you hold UK passports you will need a visa to enter Oman.
If I can assist in anyway with more information, please do not hesitate to get in-touch.
T: 020 7720 8484
8 The Boulevard, Balham High Road, SW17 7BW
(opposite DuCane Court)