Toilet is about 9 years old... just recently would overflow if my 8 year old goes to bathroom (#2) but also just started to flush twice with each use... never did this before... tonight my 3 year old used the bathroom (#1) and it overflowed and flooded bathroom... any ideas? Blockage or need new toilet?

It sounds like you have blockage, use a plunger if that would not help then use a toilet Auger, see the images below, good luck.

John

8 year old huh, boy or girl? When they go to the john next time hand them 6 squares of toilet paper and lets see if it still gets plugged. One of my kids when little started using about 20" of toilet paper each time, I had you toilet issue too.