Is it possible for a dairy allergy to return in a two year old?

Possible: The child may not have a true allergy in the first place. Initially, the child may have had milk protein intolerance, which is not an allergy.

Return ?: A true dairy allergy is usually long term and very rare in young kids. Intolerance to the sugar in dairy (lactose intolerance) is relatively common at any age and most often expressed with milk while low lactose products like sharp cheddar cheese is well tolerated (would't be if true allergy).You can develop true allergy at any age.