tourism in oman (Muscat)

Dear all,
We're living in Ethiopia and we'd like to visit Oman for one week. Any recommendation on what we could possibly do in one week would be appreciated (diving, desert, trekking, restaurant etc...). We're travelling with our 4 years old son. Is mid April a good time to come? (in terms of weather?). Any recommendation on nice and charming hotels, reasonable price (not big luxury hotels)? Thanks a lot for your advices :) Delphine