Last year I shared this great activity:
A few days later, my colleagues from Erich Kästner Grundschule (they are great) put it into practice:
Last week, I came back to that idea. I spoke to my 2nd grade students and asked them to invent a board game about addition and substraction using LEGO. I told them 1st grade student would later play the games invented by them. They really liked the idea. Here you can see pictures of them, fully engaged on creating the games for their younger friends:
Of course, as you can imagine, first grade students were also very happy when they entered the room and found the games ready for them to play...