It seems strange that Kinder Surprises (Kinder Eggs) are banned in the USA because they are considered dangerous and yet there are such things as children's guns.
Guns (unfortunately) have a much more powerful lobby than candy eggs with a toy inside.
People need to disavow themselves of the idea that everything happens uniformly in a country this big and this diverse with a dedication to individual and state autonomy. I'm sure the same people who advocated for banning candy eggs as a choking hazard would also not want kids to have access to guns. But they don't get to make all the laws. They can only pressure Congresspeople or state legislators to pass the laws they want, with varying degrees of success.
Your country is able to have a uniform law when when it comes to choking hazards so I don't think it should be impossible to pass a law prohibiting either the manufacture of children's guns or else a law setting an minimum age (maybe about 10 or 12) at which a child can use a gun.
In Australia guns control was a state issue, and we also have a powerful gun lobby, but we were able to reach agreement on banning certain guns. I admit we only have 6 states and 22 million people but the laws we reached agreement on were much stronger laws than just banning guns for small children.
You must have some federal laws that relate to the manufacture/importation of certain items (beyond a federal law that forbid eggs that contain toys).