。
She baked the kids cookies.
Literal
She [topic-は] children [target-に] cookies [object-を] made-for.
~てあげる adds the benefactive shading to 作る ('make') — 'made (cookies) for them, as a kindness.' The recipient takes に. クッキー is a katakana loanword from English, used for the imported sweet biscuit specifically — distinct from 煎餅 (rice cracker), ビスケット (the British-style biscuit, also a loanword), and traditional Japanese 和菓子. Home baking carries a particular warmth in Japan: not as routine as in some Western kitchens, since the average Japanese household oven is small and many traditional sweets don't require baking at all.