This trail is actually on the US side of Waterton-Glacier International Peace Park, however you can only reach it by boat from the Canadian side of the park.
Take the boat from Waterton Park townsite to the Goat Haunt Ranger station on the US side of the park. Check US Customs rules prior to boarding the boat! There are several hikes that originate from this location. The Goat Haunt trail is straight forward, not steep and suitable for fit children (I did it with a 3 & 5 year old). The elevation gain is about 245m and there are nice views from the Lookout.
Just make sure you are back in time for the ferry back to town.
Directions:
The Ranger at the Customs station can point you in the right direction.
