I also stated at Penisula Excelsior last summer. The room is quite "old" but the other parts of the hotel are fine. The service is satisfactory and the breakfast is foc for kids. I noticed that there are several newer hotels around, you may check with the travel agent.
Since Singapore is very small, the hotel's location is not too matter provided it's in the town area.
Also, I would suggest travelling by taxi to the airport and all scene points (e.g. zoo, bird park, sentosa, discovery centre), they are within 20mins distance and cost only around S$1x. Don't follow the tourist guide booklets that tell you how to take MRT and bus, which will spend very long time and even more expensive than taxi if you are a group of 3-4 people.