“San Juan points out the problem of disciplining the small child. He tells us, for example, that it is not reasonable or practical or good that the small child should simply do as it pleases. That it should have opportunity for self-expression is good, but that it should grow without discipline, means that ultimately it will place a heavy burden upon society. It is not good that the child should regard every restriction upon its action as a frustration. It must learn to recognize that many so-called frustrations actually are, or must become, voluntary sacrifices for the common good.”