These bikes are tough as anvils. 3 speed clutchless with throttles that can be "governed" so they are perfect for first timers but the bikes can be tricked out to the point where adults can play Travis Pastrana and still not break em. They only have two real flaws. One is that the fuel passages are so small that they get gummed up anytime they sit for a long period. They are pretty easy to drain but it is still a pain. The other is that some kids will outgrow them fast. My kids are both on the large size, my older kid went from riding the 70 4 or 5 times to now riding either a vintage 175 or his mom's TTR230. If your kids don't have shoe sizes bigger than their age the bikes rock.
The 50 is older but probably has less miles on it. 100% stock and has a new set of Metal Melisha plastic to go with. This bike would look brand new with that installed and new tires. I doubt it will start without the carb being degummed but I will give you your money back if you find anything other than that wrong with the engine/trans. It is currently in Corona. I don't have the title (but I did when I bought it). It is prohibitively expensive to try to register it in Calfornia, the back fees are hundreds of dollars so I never had them put in my name. Training wheels can be purchased but they are they are a good way to break an ankle.
The 70 has title but never transferred to my name. Same deal. California wants more money in back reg. fees than I paid for it. Slightly bigger bike but not a lot different in power. This one has a few scrapes but it is a 10 yr old kids bike. This one is here in Redlands. I think it will start but it hasn't been ridden in over a year or more. The Big Gun pipe is a real help for letting the bike rev higher and is only slightly louder at less than full throttle.
I'd like to get $400 for the 50 but I really want to see someone else's kid get turned on to dirt bikes and I don't want to work on it to get it running. Been there and done that too many times. Price on the 70? I dunno, $500ish?