Here is a quote from Mary Englebreit on the topic of licensing for artists:
On licensing agreements:
"You have to remember that you're the one with the talent who's offering the licensees the gift to be cashed in on. You're certainly bringing something to the table, too, which you're entitled to be paid for. Always try to keep your copyright. Retaining the copyright is crucial. Plus, it's important to sign the contract for the shortest time period possible. That gives you more control if the product isn't as nice as you had hoped."