Although this is a traditional children's game, in my experience it is also great fun for grown-ups! One person is Grandma - he/she faces a wall. The others in the group start at the other end of the room, then try to creep up to Grandma and tap her on the shoulder. However, at any moment, Grandma can turn around suddenly. If she sees anyone moving, she points at them and that person must return to the start. No-one is allowed to move while she is watching them.
Whoever manages to tap her on the shoulder becomes Grandma (male or female) and the game starts again. It's a good activity for cultivating concentration and patience - not to mention lots of cheating!
This is a fun introductory warm-up and concentration game. You can begin sitting down or standing up. In pairs, face each other. Start counting from one to three between yourselves, over and over. Once you get the hang of that part you are ready for the next stage. Instead of saying the number "one", you should clap your hands - but you would still say "two" and "three" aloud.
Once everyone has mastered that, the next step is that instead of saying "three", that person should bend their knees. You should still clap your hands for the number "one". This is a bit like trying to pat your head and rub your stomach at the same time - in fact, you could try that afterwards!