Because of their focus on business travelers, hotels in Singapore are not especially geared toward children. You can get extra beds in hotel rooms (this can cost S$15-S$50), and most hotels will arrange a babysitter for you on request, though most ask for at least 24 hours notice. While almost all hotels have pools to keep the kiddies cool and happy, none have lifeguards on duty, and only one hotel, Shangri-La's Rasa Sentosa Resort, has activity programs specifically for children.
Children have their own special rates of admission for just about every attraction and museum. The cutoff age for children is usually 12 years of age, but if your kids are older, be sure to ask if the attraction has a student rate for teens. If the kids get antsy during the cultural aspects of your trip, the best places to take them are the Singapore Zoo and Night Safari, the Singapore Science Centre, Underwater World on Sentosa, and Escape Theme Park and Wild Wild Wet. I can almost guarantee that your teen(s) (and you) will have a great time at any of these attractions.