Edinburgh's Royal Lyceum Theatre has managed to turn both pieces of advice on their heads with admirable performances from a dozen and more kids in The Maiden Stone, a play by Rona Munro.
The children are collectively called Bidie's Brood, named after Bidie, an auld-farrant, gang-aboot tinker bodie ("an old-fashioned, itinerant travelling person" in politically correct speak), who seems to be wet-nurse to most of North East Scotland, where the play is set.
Skilfully choreographed by Liz Mackie and sensitively directed by Steven Small, the Lyceum's education officer and assistant director for this show, the brood bring an extra dimension to the production.
The children, who all come from Lothian schools (late primary and early secondary), rehearsed intensively over five weekends. Their involvement in a professional play is, says Steven Small, "a natural extension of the regular Lyceum teach-ins and workshops".
The show is about a travelling theatre company trying to scrape a living around bothy country in the early 19th century. The story's landscape, with its Pictish standing stones, is to be taken as both natural and supernatural - an attempt at magical realism.
Bidie's Brood might well be the Devil's children (the script hints) and the Devil might well be a tinker chiel (the script hints), but it is the direct story-telling element in the play which convinces rather than the somewhat convoluted and self-consciously "mysterious" semi-supernatural sub-plot.
When Bidie (an excellent Ann-Louise Ross) spins her traveller's tales to her bairns, or chides and cajoles them, she can take the audience anywhere and imbue them with this sense of magic. But when magic - or the supernatural - impinges directly on the action in the form of Nick (Devil or tinker), you pays your money and you takes your chances.
We do see elements of feisty comedy and gritty realism, evident in Munro's Bold Girls, a set text for Higher English, but I'm not sure they quite belong in the Celtic twilight atmosphere of this play (even given Irene MacDougall's sparkling performance as the brave, foolhardy actress Harriet).
One can only wish more power to the Lyceum's elbow as regards its imaginative educational programme, which includes Saturday workshops for eight to 18-year-olds in May and June as well as week-long workshops in July. Places on all these courses are limited.
Two of the children in Bidie's Brood that I spoke to about their experiences hurled superlatives at me. Can't be bad, Mrs Worthington. Book them in now.
The Maiden Stone runs at the Lyceum until May 17. Tickets and workshop inquiries: 0131 229 9697