Birthday in a Box is your online source for party supplies and party kits. The emphasis is on children parties but we have many themes for adults too. Birthday in a Box was founded in 1996 with the goal of making it easy for parents to host personalized parties that are affordable, fun and educational. As parents of young children.We know how difficult and time consuming it can be to put together a birthday party. Birthday in a Box is your online source for party supplies and party kits. The emphasis is on children parties but we have many themes for adults too. Birthday in a Box was founded in 1996 with the goal of making it easy for parents to host personalized parties that are affordable, fun and educational. As parents of young children.We know how difficult and time consuming it can be to put together a birthday party.