Mislav has a great way to fill up the yard with balloons using golf tees to anchor them into the grass.
Get the instructions here:
http://mislav.uniqpath.com/2012/05/railsberry/
And babies make four forms the balloons into the birthday number.
Get the instructions here:
http://www.andbabiesmakefour.com/2011/01/fairy-tea-party.html