If I were to take kids into the Wind Rivers ( I have in the past), I would not choose the Highline Trail out of Green River Lakes. There have been grizzly problems there in the past. In addition, I never took my small kids in areas with big rivers. It just depends on how closely you can supervise the kids and if your kids are the type that stick around or run off or if they are more timid or daredevils. Mine were daredevils.

When in bear country (particularly grizzly country) you have to be always on the lookout for bears. Personally, I find it difficult to keep track of both bears and kids. You also really need to carry bear spray, another 11 oz and you MUST keep it away from the kids. If in addition you are not an expert backpacker, all that plus dealing with weather, etc, etc, is quite a bit of stress. A lot of people take kids into bear country. Certainly can safely be done. Just not my preference. Others here obviously disagree.

Here are a few web sites with statistics on grizzly bear encounters. There are many more. The IGBST is THE agency that deals with grizzly bear.

http://www.backcountrychronicles.com/grizzly-bear-distribution/

http://www.standard.net/Environment/2014/09/28/Are-bear-attacks-on-the-rise

http://nrmsc.usgs.gov/products/IGBST

By the way, in many Canadian national parks, where there are more grizzlies than in the USA, many trials specify that you must go in groups of four or more, and SMALL CHILDREN do not count. In other words, minimum of four adults.