A group of siblings work together to pick primroses. This vintage image of children is copyright free and would make a great image for cooperation or just of brothers and sisters playing nicely together.
Harrison Weir (1824-1906) is the illustrator of record for this circa 1880 children’s book Pictures and Prattle for the Nursery.
This image is copyright free and in the public domain anywhere that extends copyrights 70 years after death or at least 120 years after publication when the original illustrator is unknown.