It has happened.
It is possible but bad for everyone including the parents and the baby.
It's not a good idea, but in some cases it'd be possible.
No. It's not possible for a 4 year old girl to be pregnant since her body is not developing yet, and it's impossible to hold the baby when you're that small.
It is possible if that 9 year old boy/girl is good at something that people would enjoy.
No
It is almost always impossible. If a three year old has a genetic disorder that causes it to mature and hit puberty as a toddler (extremely rare) and the three year old is raped, then I guess it is possible for a three year old to have a baby. Although the three year old (if it was a girl) would probably abort or die during pregnancy, when the baby inside of it started to become baby-sized.
YES!
NO, that is not possible.
baby sitting
The question is a little vague, but in general it's at least theoretically possible that a 12-year-old girl could have a baby, or that a 12-year-old boy could father one. The youngest person on record ever to give birth was Lina Medina, who was 5 years 7 months old at the time.
It is possible
No but the sex to create that baby is illegal.