u/False-Elk9564

So we scored my son a Specialized hotrock 16" for $30. We then found out theres a local bmx racing track nearby and we brought him to a practice session and he did pretty well on the entire course for a 4year old. Is this bike a decent platform to build off of? he would love building it with me and racing. Where do I go from here? chainring? cog? hand brake? narrow tire / wheel? Any guidance would be helpful, thanks.