The urban farm in Dundrum ( Airfield) is a great venue.
Its a real urban farm, with plenty of space for a walk and lots of animals to see. I dont know what description you heard, but they have a small garden shpp, but there is a lot more to it than that.
Another option is [broken link removed]
The Phoenix Park has a good playground (at the NCR entrance) and plenty of places for a walk, with a chance of seeing the deer.