Our local stables do a pony party for 3-6's. It's 30 minutes on a led pony then the use of the decorated gazebo for the party tea and games.
Here's the link:
www.malabarriding.com.au/birthdays.html
And here are the views:
www.malabarriding.com.au/trailrides.html
I know DD would love it, and the gazebo will be wonderful. It will be the height of summer here, so no worries about weather (aside from the sun - will do 3-5 prob). All the other parents I've polled have said that their DD would love it but I think it will be a problem for quite a few parents as one parent has to do the pony lead - so it makes life awkward for those with younger siblings (ie most of them).
What do you think? Good outdoorsy alternative or a complete pain?