What is a safe motocross bike for a 12year old beginner?

yamaha ttr 125. easy trail bike to learn on, you can pop the clutch all day and it wont die. its big enough for him yet not very powerful. look at the ttr 125

mabye a tt-r 125E would work

You said motocross bike, but did you mean just a dirt bike in general? Any motocross bike is going to be fast. You didn't mention height which is a big factor. If you just need a trail bike right now, not a race bike, the Honda CRF-F line is perfect. They make a 50, 70, 80, 100, 150 and 230. No other company offers such a broad range of trail bikes. The CRF80 or 100 should fit them perfectly and aren't very powerful at all. Good solid reliable and low maintenance bikes.

well my advise is that the cc of the bike doesent really matter i know it sounds crazy but you control the speed so as lond as you dont go mad or go in a really high gear your ok, i got my bike when i was 11 and it was a 125cc pit bike id never ridden a bike before but had the basic idea, theyre much better than the top name motocross bikes as pit bikes are smaller and better for begginers. also they so much cheaper because you can get a brand new 125cc pit bike for around 350 pounds where as a top bran honda or whatever is like 500 - 1000 for 1. Hopw i helped

Have him keep riding that 50. Then put him on an 80 he will get hurt no matter what we all do, and if you buy too small you will be out buying soon again, he just has to ride and get used to it

A really great bike that would be great for a beginner is a Honda 70. The link is below: http://powersports.honda.com/2009/crf70f.aspx

pw 50 is a great starter bike, its automatic and not much more powerful than a 5 horse mini bike