I'm biting the bullet and selling my sons' bikes. They've both moved on from these two great little bikes.
My son got a Puky balance bike when he was 3. It was expensive new, but it's been through two kids and still looks almost untouched. Solid, easy to ride, good for age 3-5, but even 2 year-olds can get around on it. PUKY
When he turned 5 he graduated to this awesome Apollo BMX, which has some pretty serious gear on it including Cane Creek headset and 14mm axles. Total overkill for a 16 inch bike, but he's loved it for nearly 4 years. Scratched and scraped but still with many years left in it.Tyres and seat are A1. BMX
The two together would make a great combo to get your kids riding. I hate to part with them but I'm not having any more kids, I'm too big for them, and they're taking up space that could be filled with more appropriately sized machines. Will consider a swap for a MTB suitable for a 9 year old.