What do children who are adopted do for culture projects at school?

Next month my daughter's school is doing an International Luncheon where the students have an assignment to bring in a dish from one of the cultures of their ancestors. I am wondering what children who are adopted and don't know all their heritage do? Do they do whatever their adopted parents are? My daughter is not adopted, but I am just curious. When my son gets in that grade, only half of his lineage is known.