Masks. From Frankenstein to bunny rabbits, download the kids' masks to print and make themselves.
The more involved games come at a cost but it is usually nominal, a few dollars at the most and you have a unique game to keep the guests entertained. The best board games to be found are usually question and answer games, where the guests partner up and try to answer questions about the couple or each other for points or spaces on the printed out board. Many games are able to be customized so that you can enter specific questions about guests or the expectant parents to print out.