Ibn Umar (may Allah be pleased with them both) narrates from the Prophet (peace and blessings be upon him) that "he prescribed sadaqat al-fitr as one sa' each of dates and barley on behalf of the young and the old, the free and the slave."
I found it like this in my book: "on behalf of the child." And Imam al-Bukhari (may Allah have mercy on him) narrated it in his Sahih from Yahya, and he mentioned 'ala (upon) in place of 'an (on behalf of).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7676