It called get out a pencil and piece of paper!

 I'll bet my Mother knows this answer. She is OkieGranny on this site and as I recall she used to make crossword puzzles for my kids when they were small. She might be a good resource for you. I'm new to this site so I have no idea if you can somehow ask her directly or not, but if you can she goes by OkieGranny.
Good Luck!
Anytime-

 Auntimaime called and told me your question.  I hate to tell you this but hellopeopl is right.  That's how I did it.  One thing I found helpful was I got a puzzle book from Dollar General or Family Dollar, they have them in all sorts of categories.  Now, this is important, you can't use their puzzles.  This was just to give me the "form" so to speak.  You know, how many spaces.  You still have to come up with your own words and clues.  That was at least 15 years ago when I made the puzzles for my grandkids and I'll bet there are better ways now.  Take a trip to your nearest Office Depot or a store like that and ask if they have anything that would help you.  There may be compurter programs for it.  BUT... It's not going to be free.  For free, it's the old pencil (do not use a pen!) and table and your thinking cap.  I've done it so it can be done.  Start with common 3 - 5 letter words, that's the easiest.  Godd luck.