Who's Your Daddy? is the nineteenth episode of Season 4.
Timmy wants to go to the "Father and Son" camping event, but his dad flies away in a flying squirrel suit (for work). Timmy wishes that his "dad" would be somebody else. The problem is: each dad who he tries has something annoying about them. Who will be the "dad" to join Timmy at the father and son event?
Before Timmy and his dad go camping, dad flies away. Timmy wishes for A.J.'s dad as a substitute dad, for the "father and son" event, because he plays with giant mechanical robots. POOF! His Albert Einstein alarm clock wakes him, in A.J.'s room. A.J.'s dad comes in and Timmy, wearing A.J.'s signature sweater vest, asks him if he would accompany him to the Squirrely Scout Camp. A.J.'s dad says no, because it would be too dangerous. Instead, he goes virtual camping with his device. Timmy needs a "dad" for the event, so he trades dads with Chester, because Chester's dad isn't afraid to get dirty.
Timmy wakes up because a rat slaps his face with its tail. Chester's dad drags him to the Dimmsdale Zoo to get some breakfast. Hungry for some cheap food, Chester's dad then grabs several meerkats from their cage, wanting to fry them up for his meal. He then notifies Timmy about another good eating spot: the Dimmsdale aquarium, a.k.a. the All-You-Can-Eat-If-You-Don't-Get-Caught Buffet. Timmy then realizes that none of his replacement dads are working out for him, so he decides to trade his dad with Sanjay's stepdad.
Ridiculously early, at 5 a.m., Timmy is abruptly awoken by his alarm clock, which loudly plays the Reveille. This also reminds Cosmo of him time as a fairy scout. A flashback of him is shown waking up the old lady fairy telling her it's 5:00 and poofs up a clock that lands on her and she angrily yells "This says 9:00, you idiot! I was supposed to take my medicine 4 hours ago!" before passing out. His stepdad, a U.S. marine, makes Timmy do hundreds of backbreaking exercises. After the crazy workouts, Timmy decides to switch back to his own dad. Depressed that he has no one to go with him to the Squirrely Scout Camp, Timmy is cheered up by Wanda who tells him that maybe he should try to find someone other than a dad. After seeing Mom's resourceful skills, Timmy decides to bring his Mom with him, and thanks to her skills, they win the trophy at the camp. Wanda is glad to say "Another happy ending" to Cosmo then the old lady fairy shows up to yell at Cosmo again before passing out. Timmy then thanks his mom so much. He wishes his dad was there to see it but his mom is sure he's busy doing something important. Lastly, two Jet planes are seen chasing Mr. Turner with one of the pilots telling him "Unidentified aircraft, you're in a nut-free zone. You must land!" and Mr. Turner lastly says "Oh Nuts!"