the CRF 150F is WAY too big for a four year old unless she is much bigger than average. Start her out on a PW 50. Even if it is a little undersized, she will enjoy it more and not be scared of it. The 150 is too much bike. If she can even reach the footpegs, I'll bet she won't be able to comfortably hold the bike up with her feet on teh ground, and she most definately won't be able to pick it up. The 150 is a mid-size bike, just shy of a full-size MX machine. Too big for a 4-year old. You can find a used Pee-wee 50 (yamaha) for next to nothing, and it will be a good starter bike to make sure she likes it before you buy the more expensive 150 once she is actually big enough to handle it.
A CRF 150 is what I would buy for my wife if she wanted a dirtbike, not for a 4-year old.
Not only that, but the CRF requires her to be able to use a clutch and shift gears, where the PW is auto-clutch shifting. This is just too much for a four year old to handle...
ON EDIT!!! That said, i now realize that the 1 in 150 is acutally an F, and was a typo. The CRF50 is perfect for a four year old. It is comparable to the PW50 I was talking about. It won't go fast enough for her to really hurt herself, and is so small that she will be able to handle it. This is NOT an unsafe sport if she has the proper supervision and safety gear. That 50 just won't go fast enough for her to get hurt.... It is no more dangerous than riding a bicycle, (or even better, considering that usually, riding the motorcycle will be under more controlled curcumstances and more supervision than the bicycle)...
