Thanks for all the advice and histories, esp. Che's comments as a Mom.
Also, fully concur with comments re: abiding by son's, DILs wishes. I'd let the 4 YO use the hatchet as I'd caught him trying to use a 5 lb. axe! He's really aggressive, grandma (DW) couldn't find his dad once at 4 YO cause he was 100 ft up in a D. fir tree!
Do let all the GK's (with son/ DILs concurrance -- youngest GK 2 YO) run the track loader (full ROPS/FOPS) while sitting on my lap. 9 YO GD lifted a 42 in dia 15 ft wet cottonwood log and dropped it on the front cowl (bounced off another section of the log), no even close injuries but 2 hours of welding for repairs!
Self: too poor when a kid for Pop to own a chain saw, but had more than a few misery whip sessions. First ran CS when 23, 137 stitches when 25. (recall the old external roller bar tips? , believe they were recalled/discontinued due to my insurance claims).
DL has not yet allowed any firearms sessions.