a good size quad for an avrage sized 12 year old not a fat one is a 125cc for kids
90cc
i would get a 1cc since your probably a fail. lol
An ATV.
depends on how "big" the four year old is
Depends on the size of the 10 year old.
Yes
110cc med size Try a 200cc Yamaha Blaster with a throttle limiter. After the rider becomes more experienced remove the limiter.
ok that is a good size and you are lucky i have that size to also i am 12 years old
No.
About average
old age .just a year is enough.
im a 12 year old i have a 250 but i can easily handle a 500 but im been around them my whole life and rode since i was 3 and ive raced junior pro so i say a 300 or a blaster 200 or a raptor 250 the raptor is probly the best chioce though