Message pediatrician about it to be sure!
Before formula powder, powdered milk is what people used to mix up for their babies from birth. My mum could breast feed me so I was given normal powdered milk. Obviously it’s not ideal now that we have so many more appropriate options, but a little powdered milk in their porridge isn’t going to hurt them unless they are lactose intolerant or on a special diet.
Full fat milk for babies x