Use a digital camera to take photos of your children's faces from about the same distance for each child. (Frame you image so that their face takes up as much of the screen as possible.) Then print out an 8.5 x 11 of their picture on regular paper.
Using either lego bricks or ordinary wooden blocks, stack them together on a table so that when turned on their side there is enough surface area to cover the 8.5 x 11 picture. Mount the picture onto the group of blocks using either a glue stick or double sided tape. Then have an adult with a razor blade cut the picture apart along the seam of each lego or block.
When finished, you’ll have a puzzle to resemble each child's face. Kids will have fun, not only trying to put the puzzles together, but also mixing and matching different blocks of different children to create strange new composite faces. This makes for a fun activity to do with a new class at the beginning of the school year.