Use the Arrow Keys or WASD to move. Your goal is to bring one present to each child. 

If there's a gift on the ground, press SPACE, C, O, or U to grab the present and press the key again to throw it. If you're carrying a gift, you can't jump as high as you normally can. In some levels, you have to press switches to open gates and release the presents.

You can also jump on gifts to reach higher places.