Planning for My Little Guy's Birthday

I am starting to plan for my little man's fourth birthday which is at the end of March.  I am so excited to have a "real" party for my boy.  All of his parties so far have been at home with just family members as guests.  We decided to have his party at a local nature center that also has a petting zoo.  This place is AMAZING.  All of their animals are rescued or injured animals that they nursed back to health and all of the money for admission goes straight to salaries and supporting the wildlife there.

I am trying to do this as eco-friendly as possible.  I want to get him some recycled or natural toys, but I find that after a certain age, there isn;t as much to choose from in the toy department.  He is too old for plain wooden toys and I am trying to stay away from plastic as much as possible.  I love Green Toys Inc.  I am going to get him the Recycling Truck from here that is made from (what else?) recycled plastic milk jugs.

I am having a tough time finding other age appropriate games and toys that are "green."  I also have to find some eco-friendly party favors to hand out.  I was thinking of small pots, dirt, and seed packets so the kids can plant their own veggies when they are home, but I don't know how that would go over with the parents.  I know I hate bringing home bags of junky plastic toys and candy, but I don't know if other parents actually like that sort of thing.  I fear I may be in the minority.

Would this be appreciated or an annoyance once you got home from a birthday party?  It is a recycled Cardboard House Kit from Green Party Goods.  Problem with these are that they are $6.99 each.  A little pricey when there are a dozen children attending.

What kind of ideas do you have for eco-friendly gifts and party favors?