For a 4-year-old who's already mastered a 3-wheeler and is ready for 2 wheels, the Micro Sprite is the community's top recommendation. It's a proper 2-wheel scooter that won't embarrass them as they grow.
I too think a 2 wheeler is a bit advanced for a 4yr old, but every kid is unique. I would look at the micro sprite scooter for 2 wheels.
The most recommended kids scooter across Reddit and expert reviews for ages 2-5. Lean-to-steer design builds balance naturally, and the quality is noticeably better than cheaper alternatives.
Wirecutter's top-rated kids scooter and the best option if you want to buy once and grow with your child from age 5 through 12. Smoother and faster than anything else tested.
A well-loved budget alternative to Micro that real parents recommend. Kids consistently enjoy them, and they hold up well enough for everyday use.
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.