The Bunnings Workshop community can help with your home improvement projects.
If you wish to keep the timber finish on a wooden highchair, I suggest using Cabots 1L Clear Gloss Benchtop Timber Finish. It is food safe (once fully cured) as well as non-yellowing and heat resistant. I recommend a minimum of three coats so that it will have a tough finish.
If you are wanting to painting it a different colour, I recommend a hard-wearing finish such as Dulux Super Enamel or Dulux Aquanamel. These products achieve their non-toxic rating after fully curing, so it's important to give them enough time until the paint is totally dry before using the highchair.
Please make sure to wear personal protection such as gloves, goggles and a paint mask when working. - EricL
Workshop is a friendly place to learn, get ideas and find inspiration for your home improvement projects