http://www.nickjrbirthdayclub.com/ -select the character you want to use and fill out the form to get a Free Nick Jr. Character Birthday Phone call. They have Dora, PAW Patrol Chase & Friends, Spongebob SquarePants, Wally, Peter Rabbit, Dora and Friends, PAW Patrol Skye and Friends, Shimmer and Shine, Blaze, and Bubble Guppies.
Update– this is still available.