Ha ha - not the 400! well not on a mono pod anyway. He is pretty small for his age so can just about handle the above rig.
P.s he is always keen to show my photographer friends how he uses the back button focus!
Lovely Menace, but it's a double edged Sword, started both my Lads on Photography around the same time, 8-10 years old, my eldest went Video & now uses a Sony 3ccd 200 Video Camera with a Gates Underwater Housing, my younger Lad sticks to Stills, uses a 6D with a Seacam Underwater Housing, best to start saving for their increasing interests about, now.
But it's great fun to see what you started develop into a full fledged passion in your children.
Now if I could only get my wife interested.....then the next major upgrade wouldn't need quite so much.....stealth.
Same here with my wife too - she only wants to take selfies on the phone camera and is pretty happy with results - sigh!
I don't do any video myself but might get my kid a Gopro (or similiar) once he is ok with basic still photography and let him decide which one or both he wants to carry on with.