When we were assembling 400 pounds of IKEA bookshelves, Ranger desperately wanted to be in the action. He kept absconding with every unattended tool so he could imitate our actions. We weren't exactly thrilled to have a 2 year old running around with pointy tools or ramming them into our brand new furniture.
Eventually, we gave him a special screwdriver of his own (a screwdriver handle without any of the interchangeable magnetic tips). He loved it as it fit over the ends of the IKEA screws. We loved the fact that it couldn't easily gouge him or any of the furniture pieces nor could it actually loosen or tighten any fasteners.
Other posts about entertaining a young assistant: