Actually , it starts from $2 to an amount which is reasonable to you. Adult chinese dont normally squeak about the amount they received. As fo the kids, it's up to the education of the family, or parents to be exact, to respect other poeple's kind gesture like giving the kids anything with no question asked.
As far as I know, the kids will not embarass you in front of the crowd about the amount u give to them. Probably , they will show disappointment but that is normal.
About the amount u give to your colleagues , it probably means like $2 upwards but if u are a boss, somehow u have to give more.
That is the mentality here. Noone will say anything but their expressions say it all.
ps. The act of giving 'ang pow' is not because u are rich or what but it is a kind gesture to spread wealth around. It is always a' give and take' situation if u were to visit any chinese family during the celebrations.