William and Henry have no true "canon" designs in the games. William is depicted as a shadowed figure--a 'purple guy', if you will--while Henry is only depicted as his voice on a cassette tape.

In the graphic novels based on the books, they are depicted as follows.

I also have my own take on them! My William design is based vaguely on the graphic novel canon Dave Miller design, but my original concept was actually more inspired by JTHM. xD
My Henry design is based on the one drawn by my friend who introduced me into fnaf.
I really like seeing other people's designs, too!

For all of my William/Henry art, click here and here