I agree with Ayoob who says you cannot create childproof gun, but you can gunproof your child.
One of the family based education groups we are part of has a co-op class. In the last class, my daughters and I taught gun safety. There were nine other children, four girls and five boys ages 6-11.
We started with them making handguns out of Legos.
I asked them to share what they new about guns. Mentioned that guns are tools, just like a hammer, fork and knife, and a pencil. The tools are not dangerous, the person who uses the tool in an unsafe manner is dangerous.
Then went over the different parts of a Daisy 105 Buck. Then sent the gun around and had each one name a part.
We have five important safety rules: (We had them say the rule and hold their gun per the safety rules)
1. If you see a gun, don't touch it. Go tell a parent or other adult.
2. Keep your finger off the trigger.
3. Point the gun in a safe direction.
4. Check if the gun is loaded.
5. Check the area around the target.
My daughters came up with a song to the tune of BINGO:
"There was some kids who knew gun safety
and IKPCC's (ik-pic) in their memory.
I K P C C, I K P C C, I K P C C
and IKPCC's in their memory."
(IKPCC is the letter of the first word in each rule.)
They then made targets out of paper plates and I took two at a time into the garage to shoot their target. A couple of the boys had their own BB gun and their groups were tighter than the others. One of the girls had been around guns while this was the first gun one of the girls had ever shot.
To test rule 1, I had another room with toys that we sent the children in one at a time. My daughter was in there and would say, "Do you want to see my gun?" Only two of the nine kids went out of the room and told their parent. Others said, "Cool!" while looking at the gun.
I re-emphasized the importance of getting out of the room immediately and to go tell a parent or adult.
I then brought out a .22 revolver, 9mm pistol, 12 gauge, and AR15 and had each go through the rules in handling the guns. Though most obeyed rules 2-5, one boy familiar with guns had trouble keeping his finger off the trigger.
Overall, it was nice to have the kids hear gun safety rules, practice them, and have fun shooting. But safety rules are not learned at one sitting. They need to be taught and reenforced periodically.