Depends on the age of the kid. At the start of the trail there's more of a steep elevation with some rock "steps" that a 4-6ish year old may trip on if they aren't helped. It's not extreme. The trail can get crowded on a busy day. The Issaquah high school route of the trail is wider and less of an incline. I did see a momma bear and cub on that route of the trail last year, just as I turned a corner even on a relatively busy day. Just be aware of that. Another scenic option that's good for younger kids is the Twin Falls trail in North Bend.
The full route all the way up to poopoo point is not for kids. Especially if they are not active.
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