I bet you can do a search and see how others have done birthday parties.
I have had parties w/ other dogs and we always did little goody bags for them to take home (Healthy, top quality dog food samples - or a package of our favorite treats - a small toy (either a plush squeaky toy or small ball, etc) - a Merrick's Flossie or bully stick). Course, even one item is good enough...instead of a bag full.
I also made doggy cupcakes for each guest, and each guest had their own bowl of water (I am crazy about my two having their OWN bowl and not drinking after another "friend")
OR if you have a doggy bakery close by, that's a good place to find birthday cookies, cakes, etc. OR check out some fellow YTer's for treats, etc.
I didn't do games...but we played out in the yard and want on a little hike/walk.
Depending on the dogs...you may want to have the party outside in a fenced in area. That way, there will be no mess in the house, accidents or maybe territorial issues (lets say, a friend taking a favorite toy or something like that).
For parties for the dogs, I kept the human food simple...no cooking out, etc...just easy finger foods and drinks....and of course, human cupcakes as well.
When it is just our dogs, we do a big cook out for family and friends....if they bring their dogs, that is fine, but normally, our friends w/ big dogs don't bring theirs...just the little ones...if they feel like it.
I hope that helps.