You will have enough money with 100 usd per day.
Remember people he is staying at Rhodes hall so he will not be walking to local eateries that are on the beach or nearby.
I would plan to eat breakfast there and have lunch in my room or on the verandha what I make myself and then dine in their restaurant for dinner.That is if you are planning on eating out every day.
I would definately get out on the main stretch of beach in Negril a few days maybe you could take the kids to margaritiville they have water trampolines and a mini playground and sometimes have games and things on.Also there is the waterpark very nearby at little cost