It's Ronald's birthday and Hamburglar, upset that he didn't get Ronald a present, invites everyone to a fake amusement park known as "Birthday World" to celebrate, run by an evil mad scientist named Professor Thaddeus J. Pinchworm. Everyone is amused at first, but they can no longer escape and no longer fall for the poor designs of the rides until they ride a rollercoaster which turns them into babies (both Franklin and Tika are wearing diapers) and they need to find out how to return to their original ages, even though their certain abilities are limited since they are toddlers.
Joe Maggard
as Ronald McDonald
Dee Bradley Baker
as Sundae / TV Monitor (voice)
Christine Cavanaugh
as Birdie (voice)
Kevin Michael Richardson
as Grimace (voice)
Pamela Adlon
as McNugget #1 (voice)
Lisa Raggio
as McNugget #2 (voice)
Charlie Adler
as Hamburglar / McNugget #3 (voice)
Jazmine A. Corona
as Tika (voice)
Phil Snyder
as Professor Pinchworm (voice)
Jim Cummings
as Announcer (voice)
