Formula milk

I would start with brands like I think is common, buy in small tins. Trial and error. My first started with Similac and after 2 years old changed to Nan Pro. For my second I started with Dulac, changed to Friso Gold and now Isomil Soy Based. Planning to change back to normal milk formula to avoid being lactose free or lactose intolerant. So I would say you got to watch for their poop colour, how often they poop.