In common law, trespassers could not sue for injuries. In the early 1870s, however, courts exempted child trespassers injured by industrial machinery from this rule. The development of the hotly contested “attractive nuisance” doctrine illustrates turn-of-the-twentieth-century debates about how to allocate the risk of injury from industrial accidents, which linked responsibility to the capacity to understand danger and to exert self-control. Although at first courts in attractive nuisance cases perceived children as innocent, irrational “butterflies,” they gradually reconceived child plaintiffs to be rational, risk-bearing individuals, a change reflected and accelerated by the Safety First campaign launched by railroad corporations. This reframing of children's ability to bear risk created the standard of the “reasonable child,” which transferred responsibility for industrial accidents to children themselves. Although by the 1930s the attractive nuisance doctrine had been widely accepted, in practice the “reasonable child” standard posed a difficult hurdle for child plaintiffs to overcome.