car seats are not mandatory in taxis in HK (same in singapore), but if you have a stroller than can attach one, then that's definitely the better/safer option for traveling around with a baby.
honestly, whenever someone comes over to visit from the states they bring - something from the States for us - carters pjs, pottery barn storage bins, bed sheets, towels w/hoods, swim suits, wall stickers for kids bedrooms, kitchen supplies (cooking utensils etc..). Anything name brand - Cuisinart, Wustof, Pottery Barn, LL Bean, Lands End, Ralph Lauren etc...wil be so much cheaper in the States. Of there is Stanley Market for some of the children's clothing, but selection will be different etc....