I am planning to fly to SG during holiday in April. Beside of Universal, is there any activity place that suit for 3 years old girl?

Welcome to singapore!! There are so many places you can go for a 3year old! At sentosa, you can visit the SEA Aquarium where they can see all the types of fishes. http://www.rwsentosa.com/Homepage/Attractions/SEAAquarium There is also Kidszania which is opening soon! It's a mini heaven for kids where they will 'work'. They will learn adult's skill from fire fighting to bakery!! http://www.kidzania.com.sg/ To explore further from Sentosa, you can consider going to Park Hopping! Zoo - Night Safari - Jurong Bird Park! They have a package for it http://www.zoo.com.sg/visitor-info/park-hopper-specials.html Importantly, singapore is pretty humid remember to keep yourself and ur kids hydrated!