Last night my 14mth old had a rash from pooping too much that day. So I left her diaper off after changing her so the air could help it heal... Well we were upstairs and the two little ones were running around while I was poking around in the attic. All of a sudden my 2yr old says 'Mommy, what's that? Deeder's pooped'. Well yep she sure did on the floor, so I picked her up and put her on the potty just in case there was anything else. She was a little taken back by the incident and was a little upset so I got her down wiped her up, diapered her and cleaned up the mess. She normally likes to sit on the potty either naked or with a diaper on. I'm not officially potty training her right now, but with two older sisters she is aware of it and finds it interesting. I've noticed she is about a month ahead of my other two. I noticed at @ 15mths they became increasingly interested in me going so I would pull out the potty at that time and let them sit on it when I go. At that time I also would start looking at the books so that they can start making some associations and become aware that 'babies' and 'mommy's' both use the potty.
So it's a good idea to look for cues from your children to see when they peek interest... then it shouldn't be a power struggle!