Sayyidah Rubayyi' bint Mu'awwidh bin Afra' (may Allah be pleased with her) narrates that on the morning of Ashura the Messenger of Allah (peace and blessings be upon him) sent a messenger to the villages of the Ansar around Madinah: "Whoever began the morning fasting should complete his fast, and whoever began the morning not fasting (muftir) should complete the rest of the day." She says: After that we used to fast on it, and we would make our young children fast as well. We would make toys of wool for them and take them to the mosque, and when one of them cried for food, we would give him that (toy) until it was time to break the fast.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8408