Three balloons. Daddy balloon, mummy balloon and baby balloon.
Daddy balloon says to baby balloon, "Look son, you are much to old to sleep with mummy and daddy, you will have to sleep in you're own bed". Baby balloon protests, "I like sleeping with you and mummy". "No you are not sleeping with us and that's final". "OK", says baby balloon sadly.
Two in the morning baby balloon wakes up and decides to climb into bed with mummy and daddy. He finds there is no room, so he unties his dads knot and lets out some air, and ties him up again. Still no room, so he unties his mummy's knot, also lets some air out and ties her up again. he still can't get in, so he unties his own knot, lets out some air, and ties himself up again, he finally has room, and snuggles down with mummy and daddy.
The next day they all wake, and daddy balloon is really angry. He said, "Son, I am really disappointed with you, I said you can't sleep with us and now you've let me down, you're mummy down, but most of all you've let yourself down".