In fact, bringing a helper just to stay in a hotel room will give the parents no privacy at all!!! Actually the hotel offers children program, so that leaves you some time without the older child, will this help?
Few years ago, same case with me, I brought my 4 and 1.5 years old to Bangkok without helper. It worked fine, so to allow the older to have more chances to take care of herself. As long as you don't plan a pack schedule, it is nothing inconvenience not to bring a helper.
Anyway, you better check with hotel reservation the size of their twin bed. The Shangrila in Sentosa that I stayed only provided 3.5' x 6 twin bed, so we asked for king bed alternatively, as 3.5' was too narrow.