I have suggestions here.

thanks all. I'm keeping a list of your suggestions.
No they aren't twins just friends (two single moms and our daughters). and I'll probably be bringing the stroller since my daughter has Cerebal Palsy making walking more than 3-4 blocks very tiring on her.

gumnaam has a good point about the strollers. Space is pretty cramped everywhere esp. restaurants where they seem to pack an unreal number of diners close together and subways where during rush hour there can be barely space to stand. Anyway, if there's a mobility disability I don't see much choice - a 5 year old is pretty big for a backpack. Or, just take cabs a lot.
Without a mobility constraint, I agree with gumnaam, walking is a great way to experience NYC.
Mike