For very young or hesitant 4-year-olds, a 3-wheel scooter with a removable seat eases the transition. Multiple Reddit parents confirmed their toddlers and 4-year-olds share one happily.
If your kid is on the younger or less confident end of 4, start here. The seat option removes the intimidation factor and the 3-wheel base means they can focus on fun instead of balance.
“My 22 mo old and 4yo enjoy their shared 3 wheeled scooter (with no seat). I'd definitely suggest a 3 wheel rather than an adult 2 wheel one.”