Hello, I don't recommend it for 4 year olds. My daughter at 3 years old was already starting to feel uncomfortable with it, her legs were too bent. She was tall for her age but still. The saddle can be adjusted in height, but only by a few lengths.

We bought it for our son's second birthday and he is about to turn 4. He still uses it but it has become small. The next step will be the bike!

I think that for a 4 year old boy it is already limited, mine is a year and 8 months old. I think for a 4 year old it's better with a pedal.