My stepson was OTA when he learned to ride. I removed the pedals and have the good fortune to have a fairly long gentle slope in my yard that ends with a shorter uphill slope. He spent about an hour learning to balance, steer and brake before we put the pedals back on. Another hour of pedaling practice and we moved to an empty parking lot. It wasn't long and he was doing figure 8s on the hard surface and had sufficient control to begin riding on quiet residential streets in our neighborhood.
One suggestion I have is to raise the seat a bit. For most bikes, you shouldn't be able to plant both feet flat while seated. Being able to have the balls of your feet on the ground is sufficient. Too low of a seat position actually makes a bike harder to control. Another tip is to make sure that your tires are properly inflated. Underinflated tires + low speed will make the bike want to squirm and feel unsteady.