We are having a bday parties for our girls where to get good balloon decor and kids bday cake. They are 3 and 5yrs old.

You can consider getting them from party specialists, Sprinkie Parties. They are relatively new to the scene but I've heard so many great things about what they do. You can get decorations (even personalised ones) from them and all the usual party treats. www.sprinkieparties.com As for kids birthday cakes, I love the cakes from freshbakes.com.sg -- they have fantastic cakes which taste and look awesome.