Children were bargaining chips. Children were property. Children were immortality. Children were earners of income. Adults in Jesus' time, like adults today, defined children in relation to their own needs and wants.
Children are dependent persons whose lives are defined by others.
Most adults in relationship to children, their own or other people's, shuffle through a succession of definitions during its course. To parents children can be blessings one moment and nuisances the next. To the police children can be minors in need of protection one moment and potential hoodlums the next. To media moguls children can be minds to engage and entertain one moment and easily manipulated consumers the next. The long childhood is a relatively recent invention.