My Childrens is 4 months old, and the last time I measured him, which was about a month ago exactly he was 40cm long. The time I measured him before that which was a month before last he was 36cm long. I haven't measured him lately, but I think it's had some pretty significant growth since. Actually, I might try and measure him tonight, but he's been a bit agro lately.
Just measured then and hes at 45cm!