Different charities have different rules and or requirements for their organizations. Asking a specific group or place you want to donate what they require is really the best route; however, don't get discourage there is usually a group out there who would gladly accept what you are able to donate. You could also try asking at your LYS (local yarn store) or a local shelter (homeless or women's). A general rule I normally follow though is that for very cold climates for children and adults I use wool either worsted weight or bulky. For preemie hats, blankets, etc. I use cotton or man-made fibers, and for in-between type chartible knitting depending on the item I use a wool-man-made fiber blend or a soft man-made fiber.
I am not able to locate a youth jester hat pattern; though, you might want to look at this pattern on woolly wormhead and possibly adjust the pattern for smaller heads. Here is the web site: http://woollywormhead.blogspot.com/2...ester-hat.html
Here are also two links for charities and charity links for places in Canada that accept donations:
Finally, you might want to post this question in the "Charity Knitting" section of this web site you will probably receive a lot more responses to your question.
Good luck and happy charitable knitting,
PS. I also forgot to post this article form Knitty: http://www.knitty.com/issuefall03/FEATcharity.html
you might want to also try the yahoo group caring4canadians. Or do a google search for charity knitting canada.