My 4 year old son just started BMX racing. He sometimes is barley making it over the hills/jumps. The problem area is later in track , when he no longer has the speed from the starting gate hill. I was thinking of changing his gearing, but I’m unsure which way to go. He is riding a Haro CSX which came with 40/16 gears.
I was trying to decide between changing his chain ring to a 38 or 42.
I was thinking:
the 38 would make it easier to pedal up the hills, but would slow him down overall.
The would 42 would allow him to get more speed when pedaling before the hills and coast up, but 42/16 may be to hard for a 4 year old.

I need your thoughts or experiences, Because I don’t get much input from a 4 year old and this is all new to me.

Thanks for you help.