The kindergarten bought a lot of white rabbits, pandas, and giraffe plastic toys. Each child can choose two of them arbitrarily. No matter how you choose, there will always be two of the same toys among any seven children. Please explain the reason.
幼儿园买来了很多白兔、熊猫、长颈鹿塑料玩具，每个小朋友可以任意选择两件，那么不管怎样挑选，在任意7个小朋友中总有两个小朋友的玩具相同，请说明道理．
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>