My son has a few allergies to certain food, fish,dairy,oil are the main ones. I'm worried he won't be able to eat much
What would be normally eat at home?
Avoid these items in your culinary choices, that's all. Read menu carefully and ask the questions to the restaurant staff if you are in doubt what to order. Singapore is a civilized place and everyone speaks English.
Most things but not the items he can't have. Worried as it's a new place to go
I can't think of much food that has no oil other than salad and soup-based dishes. Cross-contamination will be the main issue you need to consider besides looking at the ingredients of a dish. Soup-based dishes may have cross-contamination with fish; the knife used to apply kaya may have contact with butter, etc.