You cannot hide anything from the kids. Teach rather than forbid.
Start the in depth training as soon as the child shows more than a passive interest. My oldest daughter became obsessed with daddy's guns at age 3, my son at age 3, and the other two girls were 6 or 7.
The first lesson involved a 12 guage, a watermelon and a load of 00 buck. Lesson learned on first try.
2nd lesson was their chance to shoot a real gun, mama's little ruger bearcat .22. The initial noise was also lesson learned.
Obsession went back to passive for a couple years in every case. By six years old, we scheduled regular shooting days when all farmwork stopped and we all went out to my little range. There they learned firearm safety, range safety, as well as marksmanship.
By age 12, all were proficient with rifle, shotgun and pistol, if not expert.
I took a board and drilled holes and marked each kids section. The appropriate ammo was placed in the hole before we went to shoot so each round could be accounted for. After each shooting episode, all firearms were cleaned and locked back up until the next time. (with the exception of Mom's and Dad's pistols) We never had a problem with any of the kids wanting to handle the guns or play with them as toys. They all took pride in their own marksmanship and the ability to go to the local trap club and show their proficiency with both safety rules and marksmanship.