Can not back up or even push it backwards in neutral running or not.

ONLY IN NEUTRAL CAN YOU PUSH ANY M/T CAR
UNLESS HOLDING DOWN THE CLUTCH PEDAL ENDLESS IS FUN?
OR CLUTCH IS BAD.
ENGINE IS OFF YOU MEANT. AS IN STALLED OR KEY OFF.

I do not under stand you post and story at all.
does engine run?
does engine start and run in NEUTRAL?
if yes, yes, then I bet ( wild guess 1)
you depress the clutch pedal and can not shift to any gear.
that is a bad clutch, top cause easy is , bad MC/slave to clutch
master cylinder or slave bad
and the MC fluid jar there is dry OOPS dry means MC and or Slave are bad

. I would check the shifter cable. If it broke in reverse while you're son was putting it in drive that would cause it to remain in reverse . Being stuck in reverse would also cause it not to start because it's in gear.

on the left side on you shift stick is a small cap. remove the cap and push the button with a key and shift to neutral. make sure you have the parking brake ready to prevent the car from rolling.your food brake wont hold good if the engine don't run
the best is to replace or recharge the battery.

If reverse is done and you can only go forward is it shifting out of first. If its not then you need the transmission rebuilt. That's what happened on my truck.

have you checked the back brake shoes. also check the tranfere case fluid level

You have a failed transmission. You will need to tear it down and rebuild it to replace it with a factory reman unit.

EASIER TO RUN AN EXTENSION CORD WITH A BATTERY CHARGER INTO THE GARAGE!

Do you have ignition lights.? Starter solenoid may be stuck, put car in 1st gear & rock it backwards & forwards, select neutral & try starting normally. Have you tried giving it a push & bump starting, if it runs then you got starter motor issue.

I assume it's a manual transmission.
If the car will not roll backward or forward in neutral (with or without the clutch engaged) the transmission is most likely locked in two gears at the same time.
This may happen if gear selectors are excessively worn. If you are able to examine the gear selection levers external to the gearbox, ensure they are in the 'neutral' (no gear selected) position when the gear lever is in Neutral. If not in correct position, you may be able to manually reset the levers to correct neutral position and thereby unlock the gearbox.
In any case, if it's happened once, it will happen again, so get the gearbox and gear selection mechanism checked for wear or breakage.

im sorry to say no it will not.