Hi! all,
Just couldn't help answering some of the questions. I'm a Singaporean living here so I may have some ideas for you.
The flight to S'pore is about 3 1/2 hrs only not 5 so if you are flying in the afternoon, it could be baby's nap time and by the you reach there, your baby will ready to go.
My sons still insist on going to Sentosa every time we go back for a holiday and we have only stayed at Shangri-La Rasa Sentosa but the kids just love it there. The kids pool keeps them happy all day. There's also a water theme park that opened in July last year and that's at Downtown East (Pasir Ris) Good fun for the whole family even toddlers. The Night Safari is also good and they have a speacial pass where you can go to 2 or all 3 (Zoo, Birdpark & Night Safari) for a discounted price.
If you want to sample local food besides just the chilli crab, try the East Coast Parkway Hawker Centre. You can try all the different kinds of food (Malay, Chinese & Indian) all under one roof and still get the chilli crab. Another place closer into the city and Sentosa is Newton Hawker Centre.
One more thing, it's not always rainy in S'pore, they have been getting the weird rainy weather like us here too. But generally, August is not a rainy month.One last thing, 9th August is S'pore's National Day and they have the parade and fireworks. So, if you are there, you might want to see if you can catch the fireworks at least.