Daddy, bikes cost lots of pounds....

[Markymark]

....but that's ok because I can just ask Santa for one as this one is too small!!

That's the thing with bikes for 4 year olds, they're too small for when they're 5!

 

[David Higson]

Get one sized for a seven year old - they'll grow into it!
That's what we thought when we bought our son a nice BMX when he was a child. Well, he didn't ride it very much, it rusted away in our garage to be binned when he went away to university. He picked up the cycling bug again during a stay in South Korea and he now rides some pretty long distances on his repurposed hybrid.