Hi,
My son is merely 3,5 feet tall. I have a good deal on a GT Power Micro with a 16,25 top tube. Too big? Should I go for a 18" wheels model such as a Haro SR Micro Mini or a Redline Flight Micro Mini? I think that these ones will be ok for him just one year. I don't want to keep her bikes for years or buy a too big bike in the hope of long lasting live for the bike, but I am to be reasonible and take good decisions.
He is an avid 12" rider (you should see).
Any experience, advice?
Thanks.

My son (~98 cm tall) has one of these:

http://www.islabikes.co.uk/bike_pages/cnoc14.html

It is only just small enough for him, so should last him a good few years, before mny daughter grows into it. I would think that anything with 18" wheels will be far too big.