Four is pretty young to be in the shop, but escorted 100% of the
time. Basically for an inspection tour, do NOT expect to do any
work while he's there.

I'll disagree with that. My oldest isnt' even two yet and he comes out
to the shop with me all of the time. I do restrict myself to
operations that I can do and monitor him as necessary.

He is surpisingly well behaved while out there and understands when I
tell him to not touch or do certain things. I can tell him to get
stuff and put it back and he can do it if kept in simple enough terms.
I don't expect him to get the 9/16" 3/8 drive deepwell, but if I say
get me the screwdriver right there he can hand to me. If I tell him to
put this in the bottom drawer of the tool box, he will.

He has learned to listen when Dad say's "Dont' touch that". I dont'
yell, but make a firm statement. He will look at me, I usually repeat
the statement, and he just gets this understanding look on his face.

I don't weld while he is around. I don't think he is old enough to
understand to not look at the light.

Of course he has been going out to the shop since before he could walk.

Most times he just "works" at his bench and stays out of the way. He
has a little Playschool bench and the accessory set of hand tools. He
is usually quite content to stay over there and put in his bolts or
screws or bang on things with his little hammer.