One time I had a four hour layover in SLC and went to downtown. I didn't take the shuttle bus, but opted for the city bus instead (just to add to the experience).

I forgot how much the fare was (around $1.50 probably), but the transfer time was so long, I was able to use it on the return. I was floored by the acceleration rate of these buses. Normally the driver "floors" it, and the diesel engine does the best it can, which is not much. But these Salt Lake City buses accelerate like a car!

I took the train from the Delta Center to the first stop south of the temple, which is in the fare-free zone, and walked through the temple grounds but didn't go inside. I did obey their silly no-smoking rules. If I remember correctly, they also tried to ban smoking on the sidewalk on the outside of their property but were struck down. ^

I stayed clear of the missionaries but did manage to snap a picture unbeknownst to them using the zoom feature of my camera.

I would not recommend this tour with two little kids and a three hour layover. If you had five or six hours, maybe so, but I wouldn't bother if I were you.

Walk around the airport with the kids for a while and then visit the kiddie play area, which I think is across from the Cinnabon's on the way towards E concourse.