I've heard people recommend taking the pedals off the bike, so they just scoot along with their feet. That helps them learn balance - then when they have some confidence you can put the pedals back on again.
This is exactly what I have done with each of my kids, then when I think they are close to ready I spend a couple of hours in one solid chunk running along behind holding the saddle giving lots of encouragement, then eventually let go of the saddle and that's it. I will say though that letting go of that saddle is a leap of faith that you have to learn, it's not all about the child.This, it's the quickest and painless way.
Unfortunately stabalisers seem counterproductive to learning the basic sense of bance required to ride a bike.
Once you have balance, learning to pedal is child's play!
This
This is exactly what I have done with each of my kids, then when I think they are close to ready I spend a couple of hours in one solid chunk running along behind holding the saddle giving lots of encouragement, then eventually let go of the saddle and that's it. I will say though that letting go of that saddle is a leap of faith that you have to learn, it's not all about the child.

That's what I did in a small area of grassland that had a couple of tarmac paths running through it. I still have fond memories of those long gone days when I walk across those paths.I've taught a couple of little people to ride. The best trick I learnt was to run alongside/behind the child with me holding the saddle the whole time,
Eventually, you can start to release them when they seem stable,
Flat short grass is better than tarmac to start with, for those unfortunate landings. Grass however is a pain for steering, the ruts and bumps are off putting.
A good age to start them is 4 or 5, IMO.