Children are property of their parents or the state until they
are 18 years of age in many jurisdictions.
They are the responsibility of their owners until such time that
they are deemed fit for society. They cannot sign papers. They
are not responsible for their actions. They are legally,
infants. Infante.
There are exceptions for certain things; infants are considered
responsible for certain crimes. Also, some of the protections
they have as infants they no longer have as older infants. But
they're still legally infants.