At our school we have a program where our high schoolers in year 4 of Spanish get to visit the elementary school teach Spanish to the younger kids.
I email the elemntary school looking for teachers to volunteer for the program. The high school kids visit an assigned elementary school class for 5 lessons, 30 minutes each.
I pair students together in groups of two or three so they don't have to teach solo.
They get to teach the kids basic concepts, like counting in spanish, animal names, colors, etc.
High school students must submit their own lesson plans, make all necessary posters and worksheets, and teach the lessons themselves.
I have received lots of positive feedback from administration, elementary teachers, parents, young kids, and high school kids.