Dear pregnant mothers, we have an idea for you. A baby quiz. This is how you do it: For every participant (that can be you, your partner, siblings, grandmas, grandpas, aunts, uncles, friends, just everybody you want to participate) you write on a sheet of paper:
Weight
Height
Haircolor
Looks .... alike
Name
Birth
Time
Boy or Girl

You can add things to the list or cross some off, if you already know if it's a boy or girl or the name is already set. Everybody fill the list out in secret. Siblings that are unable to work with weight and height, could say if the baby will be bigger or smaller than themselves were. Or something thats reaaally cute: Take a stuffed animal, that's about 50 cm long and the sibling can guess if the baby will be bigger or smaller. Once the baby comes, you can compare the lists.
The lists will be collected, put in an envelope and sealed. When the baby arrives, the lists can be counted in a ceremonial setting. Every right answer, or the one that's the nearest to the right answer, gets a point. All the points are counted and the winner stands.