Phineas and Ferb (2007)

S3E4 Last Train to Bustville

During their stay at their grandparents' house, the kids come up with the idea to build and compete with a massive hot air balloon. At the same time, Candace, motivated by the determined train engineer Glenda, resolves to stop trying to catch her brothers in the act. Meanwhile, Dr. Doofenshmirtz stumbles upon a Dodo bird egg and believes it to be a fearsome creature that will assist him in his plans for conquering the Tri-State area, only to be surprised by the reality when the egg finally hatches.