Setting the seat and handlebar height is important to get your child in the best position for riding. On most bikes you can adjust the height of the seat and the handlebars. You may need some tools for this; either an allen key or spanner. The handlebars should be set at a height that allows your child to be in full control; just above belly button height when sitting on the saddle is a good guide. If the handlebars are too high or too close to the body then it makes turning and balancing much harder to master. For activities on a balance bike, your child should be able to place the balls of their feet on the floor when sitting on it. There should also be a slight bend in their knees.
Things to check before you ride:
If your bike needs a bit of fixing, a family member may be able to help. If not, there are friendly mechanics working in bike shops.
You can make it into a fun game by playing musical bikes together, getting on and off the bike as the music stops. Try getting on and off on both sides!