Sizing a child to a bike

MTB-Dave
MTB-Dave Posts: 42
edited February 2012 in MTB general
Hello i hope someone can help me,

I am wanting to get my eldest child (hes 5 in march) a decent alloy bike, Islabikes seem to be highly recommend.

However what my issue is, is this:

Isla bikes is around 300 mile away from me in one direction so not really practical for a drive, so using their size chart their 16" says min inside led of 42cm however he has an inside leg of 39cm will the three cm be an issue or would you go with it?

He is a confident rider without stablisers and has been for a year

He has sat on a 16 in Halfords and seems to fit it fine however it was steel and weight about the same as a small car lol.

Any help would be great,
David

Bike: Specialized Hard Rock Pro Disc 2010