Very quickly. We had just about weaned Frankie onto cow's milk but thus weekend he has come down with the most horrendous cold. He is eating virtually nothing at the moment which I know is normal and I'm making sure his fluids intake remains high but I have reverted to giving him toddler formula to make sure he is getting some goodness. We were him Aptimal stage 3 but have run out so DH has quickly been to our Tesco Express and has brought back SMA follow on milk as it was all they had.Is it ok to give him a different brand of formula? Will it upset his tummy?