[Yosemite Sam]

Welcome to OCC.

Sorry to hear about the broken hip. That has got to be a PITA.

This sounds like a great Father/Son project.

In its simplest form an engine only three things to run, Air, Fuel and Spark.

That said, if you have spark and it occurs at the right time (unless there has been an internal failure of some sort) the only thing left is fuel and air.

Check the plug itself for spark, just to be sure.

If you do have spark at the plug then, I personally would pour a little gas into the spark plug hole (put the plug back in) and try to start it. I don't know that this would be good practice in front of a 7 year old boy though.