Ivan Riding A Bike That Is Big For Him

Ivan doesn't want to ride his trike anymore. He wants to ride the bike of his cousin. He's cousin is 8yrs old and and 6yrs old. I'm so afraid my son would fell down riding a bike. He's having a hard time climbing up and down the bike. What more about balancing and controlling the himself and the bike when he's out of balance, or bump on something. We have a small living room space for him and his bike. He's still 3 years 6 months old. Shouldn't he ride a trike instead of a bike?

Ivan Riding A Bike That Is Big For Him