I second a notion from the "child safe chantey" thread - it's not a matter of making the songs CHILD safe but rather PARENT safe. You tailor your restrictions to the parent-audience.
Even if the parents aren't present, you can probably count on the kids singing whatever they learn. So if you're looking for repeat gigs and to avoid tempting parents to seek legal action, get an idea of the tolerance of the parents before launching into anything that could be considered controversial by a "modern" (i.e. historically ignorant and hysterically protective) adult.
This also has echoes from a recent thread on "what topics should you not make songs about" - the treatment of the topic has a fair amount to do with whether or not it's offensive (humor or satire can defuse much pain & anger). Unfortunately, kids may parrot the words - and parents may hear them - without knowing (or at least without deeply embracing) the historical referent nor the intended treatment.
All that being said, there are some people who will choose to find offense in ANYthing. "When correctly viewed, everything is lewd" as Prof. T. Lehrer so aptly put it.