Check the regs before you go. The middle and north fork both have decent populations of small cutthroat. Middle fork is selective gear rules, I don't know about the north fork. Most of the lakes up there close on the 31st of OCtober, I believe.

It's getting a bit late for easy fishing up there. For kid fishing, I'd try trolling for cutthroats, or perch fishing, in Lake Washington or Sammamish.
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