Sergeant Keroro (2004)

Sergeant Keroro, a frog-like alien invader, is captured in the line of duty by two Japanese teenagers while scouting for an invasion of Earth. After being left behind when the mission is aborted, Keroro is taken in (with some reluctance on all parties) by his captors: Fuyuki Hinata, his big sister Natsumi, and their single mom Aki. Keroro quickly begins plotting his comeback, scheming to reunite with his amphibian squad-mates (the mercurial Private Tamama, the gruff Corporal Giroro, the mischievous Sgt. Major Kururu, and the enigmatic Dororo) and renew their plan to conquer Earth (or "Pekopon", as the invaders call it)... when he's not being distracted by building Gundam model kits, or by other aspects of Earth culture.