You seem to be under the impression that it is illegal to have guns and children. It is not.
If toys did not exist, children and their parents would invent them.
Children would probably look more like their parents.
Nothing "would happen". There are lots of things that might happen, depending on the exact circumstances.You would probably find it difficult to do this without their permission, though.
Tracking systems may be put on children to insure their safety, and if anything were to happen to them they would be recoverable. Tracking systems would be a great way for parents to know where their children are.
Children would probably look more like their parents.
Youd have no parents
The foster parents receive a set sum for each child from the state and the parents pay the state. Since it would be a very different sum for each child based on what parents can pay, the sum is set for each child and every state have this system. The foster parents should not have to use their money. if that was the case we would have very few foster families because they would not afford it.
Under Bolshevik led Russia, children who reported their parents were rewarded as heroes of the state and given rewards. Sometimes, in the years of state imposed famine, children would denounce their parents for food either because it was given to them by the government or because, with the parents now gone, they could do what they wanted to do. After the October Revolution when Lenin and the Bolsheviks took control of Russia, they placed emphasis on the importance of the state and practically destroyed the concept of family. They felt that family members who had allegiance to one another did not have the proper allegiance to the state. Children were encouraged to denounce their parents for any inkling of counter-revolutionary thought.
the children would miss their parents or they could be homeless on the streets
Without parents life for children in general cannot exist - unless you believe the state should house, cloth, feed and educate all children. Children need love, acceptance, discipline and nurturing. With no parent to give this children do not develop into loving, caring adults. As we know, not all parents are fit to be parents - their loss, if there could be a good, loving replacement would not be a bad thing.
They would get fat.
Nothing would happen, other than the 15 year getting into trouble with her parents. If there is sexual contact, there would be problems. It is illegal as she is under the age of consent.