to become hungry; to have an empty stomach (colloquial expression).
遠足の前日はみんなでお腹を空かせておくために軽めに食べた。
The night before the field trip we ate lightly so we'd be hungry.
子どもは帰るとすぐに『お腹すいた！』とお腹を空かせていることが多い。
Children often come home and immediately say, 'I'm hungry!' — they're usually hungry.
昼までお腹を空かせないように、朝ごはんはしっかり食べてください。
Eat a proper breakfast so you don't get hungry by noon.