I just recently ran across two parent and tot yoga class offerings

One on Saturday mornings through Pure Freedom Yoga
http://www.purefreedomyoga.com/p/schedule.html

One on Tuesday mornings at Therapeutic Approach Yoga Studio
http://www.yogastudio.ns.ca/schedule.htm

My little one is just 27 months old so I wasn't sure about trying out something like this. The class was great and used a combination of music and storytelling that incorporated different postures. The instructor was friendly and flexible in her teaching.

For the benefit of others parents - what yoga classes have you participated in as a family and what has your experience with these classes been?

We haven't experienced any classes yet, but we did pick up a great kids yoga dvd at the Seaport Market. It's called YogaKids 3, Silly to Calm for ages 3-6 with Marsha Wenig by GAIAM. There was a vendor selling it near the Selwood Green cafe, next door to the Mike's Fish.
My 2.5 year old loves it.