Asalam alaykum
Please find attached a free downloadable with some short hadith of the Prophet Muhammad ﷺ that children can learn and memorise.
I compiled these from a talk by Sheikh Abdulilah Lahmani (Markaz Muaadh):
https://m.soundcloud.com/markazmuaadh/20-hadeeth-for-children-by-shaykh-abdulilah-lahmami?ref=whatsapp-text&p=a&c=0&utm_campaign=social_sharing&utm_medium=story&utm_source=whatsapp