Help me out here!

[kitchenwitch.livejournal.com]

I'd like to make one of those kitty hats for my niece, who is 5 years old, and the bear hat variation that someone posted awhile ago for my nephew, who is about 3. How should I alter this pattern so that it will fit their heads? Or should the hat be small enough as it is? I noticed instructions on the site for a baby's devil hat, but these kids are no longer babies (and my nephew's a big boy with a head as big as his sister's, probably). Thanks for any help you can give me!