Typically, toddlers and kids enjoy balance bikes from ages 18 months to 5 years old.
buy a bike smaller than the kid can use with pedals, yes, smaller.
Then get the chain, pedals, etc off the bike. Won't use them, and they get in the way
Then the kid only needs to concentrate on pushing the bike and steering. They will have both feet on the ground as much as they like, immediately removing all traces of worrying about balance.
Bingo, they are quickly pushing as fast as they can, or want to, and going for longer glides without the feet down. Simple enough. Soon as they are comfortable, or bored with this, switch to the right size bike with pedals, and all they need to learn is pedalling and braking.
I didn't learn a bike til I was 7, no training wheels, and plenty of skinned up knees and torn jeans.
If you'd rather your kid learn early, and fast, and be far more proficient... skip training wheels, use a balance bike, and you'll see. All the experts agree. It's faster, safer, and better for cognitive experience.
see for yourself, you tube has lots of vids showing the improved speed and enjoyment of kids learning on a balance bike, here is just one, and I don't endorse the bike maker, I don't care what model or maker you buy from. I just want you to know this new way of letting kids learn to ride is enjoyable and quicker. Safer too.