My sons four wheeler has gas and spark but won't start. What should I check

There are many reasons a engine won't start but the basic staring point is to drain the fuel from the tank and the carb bowl. Refill with fresh fuel. If this does not improve starting we can go over cleaning the carb and needle valve. Have you try a spary of starting fluid in the air intake?

Gas needs to be good, spark at the right time and compression.
Has it been sitting?
Like abobe, I would suspect fuel first, any safety or kill switches?