Looking for some input, any recommendations or just find a 50cc bike and get them on it? They all basically the same?

The Yamaha PW50 is appealing to me, being a 2 stroke it’s a bit lighter than it’s 4 stroke counterparts.

Going to be for my daughter who is 6.5 and my son who will be 5 in a couple months. Both are very good on their bicycles, haven’t had training wheels for quite some time. We have a lot of property so it’ll really just be used here at least initially.

Just went through the same thing for my 7yr old. Picked up a 2005 crf50 for $800 and couldn't be happier.

I race dirt bikes and help out with the little kids program, so I see them all.  The PW50 is good for the really little ones, but it is anemic when going up any kind of incline.  The Honda CRF50 is a little bit bigger and as you mentioned heavier, but it is a much better learning bike if you plan to do any kind of trails with hills.  If you want a lite and powerful 50cc two stroke, get the KTM 50 SX, but it is $$$$.  All are adjustable so you can turn it down until they learn and slowly turn them up.

I'd recommend getting a Razor MX350 first as they are cheap and not that heavy.  I got my son one and then a CRF50F and he loved both (has a CRF110F now). The CR50 will be pretty heavy for most 5-6 yr olds, so definitely plan on it getting laid down.

Used CRF50 is working pretty well for my kids.

I’d go either the crf50 or ttr50. The pw seems small for a 6.5yr old.

My 9yr old daughter started on a crf110 this year. She is small, but handles the 110 perfectly fine. Real glad I didn’t go with the 50.

My boys started on a crf50 and ltz50 quad, then LTZ90>TRX90>TTr125>CR85r>CRF150r>CRF150r Big Wheel>CRF250x, now we're at a CRF250r and WR250f

CRF50 or TTR50 are both good, you can't go wrong with either.  I wouldn't bother with a used PW50...I doubt they would be able to pick up a PW50 either...so it's mute point.  They will all get dropped at some point...that's a guarantee.  Not even worth worrying about that.  

Don't overpay for a used one, and when they're done with it (if they don't destroy it) you should be able to sell it for what you paid for it.  Then move into the 110's

7 year old boy is on a TT-R110, he is super tall for his age though and he can touch no problem.  Last year, he rode it but I had to hold him up while he took off and he would ride it back to me so I could hold him up while he stopped.  Luckily he has really good throttle, brake, and slow speed control.  He rarely dropped it.  He rode a balance bike from 1-3 and was a beast on it.  Took it off jumps and shit.  He never rode a pedal bike with training wheels.  He went straight from balance bike to pedal bike and was riding in 5 minutes once he figured out the pedal situation.  He rides dirtbikes like he was born for it.  This kid rips trails on this thing.  

My 11 year old rides it too, but he's too big for it.  I'm looking for a KLX 140 L for him.  He's big for his age too though...I think a 110 is good for 'most' 9 through 12 year olds probably.  50s are good for 4-8 usually.

I think a PW50 is a great bike to start with. Buy a cheap one, run it for a few months while you shop for a XR/CRF/TTR50 then sell it for what you paid for it. It is simpler, lighter, and quieter than the others.

50 is a little small for 6.5 IMO. Something like a Kawi KLX 110R or 110RL would be better. The 110R has a auto clutch so they can just shift the gears. The RL had the manual Clutch and shifting.

I would disagree.  My 7 year old is very tall for his age and he can just now touch with both feet on our TT-R110.  MOST 6 to 7 year olds will not be able to touch on a 110.