E.S.
Dairy products made from cow's milk are risky. Yes, they have been fermented, but you have to realize there are many things a child could react to...the protein, the lactose, even the breed of cow can affect the chemical composition of milk and it's potential to cause problems. Older breeds like jersy cows (as opposed to the ever popular Holstein here in USA) produce milk with different chemical factors. Less reactive in some individuals.
Then there is the whole issue of what modern milk processing does to milk...some people really feel raw is best. I use raw milk cheeses whenever possible.
It's nice to know that after 6 months of age a baby's gut lining has more fully developed, thus making it LESS likely that there will be some adverse reaction, but we are all different! Good luck!