Mar y tierra is a traditional Spanish game kids play at recess. It is very simple and it can be played inside if you have enough space. It is a fun brain break that gets kids up and moving.
Traditionally, kids jump between two spaces designated mar and tierra. You can change the vocabulary if you like. For example, for Easter, you can make the kids conejitos and designate the two spaces bosque or campo and jardín. Any logical pair of words works.
To play, kids line up beside a line on the ground so that they can jump sideways over the line. They can also face the line and jump forward and back. One side of the line is mar and the other side is tierra. A person who has been chosen to call first, calls out mar and tierra as the players jump across the line (or in place) to be on the correct side. The child who makes a mistake and jumps in the wrong place is out, or not, depending on how you want to play.
Here is a video of kids playing Mar y tierra. They play without a line and it works fine too.
Here is video of a group of scouts playing. They are jumping on and off a (not so) low wall. It makes the game considerably more aerobic!
You can see an animated explanation of the game here: Spanish game – Mar y tierra
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