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I think you have to already have some kind of negative association with
"the law" to see the term "legal/illegal" as necessarily a negative one.
As I see it, there are all kinds of laws, some bad, some good, some
arbitrarily imposed by an authority, and some self-imposed and freely
chosen.  If somebody sets up a set of rules, or "law," for themselves,
and freely chooses to follow them, then "legal" isn't necessarily a
negative concept, in that context.

But personally, I prefer the term "safe."  "Safe" even works quite well
when communicating with a toddler.  (That and "yucky-for-you.")

  -- Angi