dust shouldn't cause much of an issue as long as the air filter is well maintained.
I understand that it does turn over but didn't want to pop and take over by itself;
is that correct?
if so:
For a quick pre-test
just remove the injector nozzle from the manifold,
and firmly hold it in your hand (it's tip covered by a paper tissue)
have your kid try to briefly start the engine;
you should feel it clicking in your hand and get a miniscule fuel stain on the tissue paper.
no click, no fuel and it'd be the injection not working
check the wiring harness (yes I'm afraid all of it) for broken wires and loose connections,
chances are the injector isn't firing because of a a loose/broken connection;
most likely it's just a connector that rattled loose,
could of course be either the injector itself (highly unlikely),
one of it's required sensors (IAP, MAP, CPS or such)
or the ECU which would be the worst that could have happened.
clicks but no fuel and it'd be a clocked fuel line somewhere,
at worst the fuel port of the injector itself.
clean the tank and (clean or replace) the fuel filter,
blow the fuel lines with compressed air (OFF the engine of course!!)
and reinstall everything once cleaned.
the injector nozzle is a bit trickier, let's just hope it's not it
(can be cleaned with an ultrasonic bath, but it must not be submerged and under pressure)
clicks and sprays fuel
and we need to move on..
next thing might be the lack of compression,
so get a compression tester (or your thumb as a substitute ) and see how good the compression is.
it's a rather new kart and I cannot imagine it being too bad,
but a dusty area and a badly maintained and thus failed air filter and that might indeed be a possibility.
I unfortunately don't have a manual for that kart, so I can't tell where to look first.
or give you a clue about any particular order really.
'sid
