Age 17 and below.
Edit: oh but wow I just read the order and it defines child as anyone under 19. I'm surprised they chose to just add a year of childhood in this instance. That is not typical.
You are usually considered an adult at age 18 and granted a degree of autonomy (and the right to vote). Notable exceptions being controlled substances like alcohol and nicotine that require you to be 21.
There's some rights and privileges granted to minors at 15 or 16, about driving and working. Age of consent tends to hover around 17 or 18 aside from a handful of states.
Edit: LOL @ the downvote.