We threw a birthday party for our three-year-old boy/girl twins at our home in June. We had food and drinks inside and a huge “castle” made out of cardboard boxes outside for the kids. The party was very casual and unstructured; people went in and out as they pleased, we opened presents at one point and then let all of the kids play with all of the toys, and we had a bunch of cupcakes (that people ate whenever they wanted) instead of a formal cake.