Hazel good advice. I too, am allergic to many dogs. When I looked into getting my current monster,l I stuck my face right into his fur to see if I'd react.
They should know right away if the child does that to an adult dog. Adult, not pups. Pups have baby fur.
A good breeder would not want to sell a pup knowing the new family may have to get rid of it right away.
(ps what is an OES?)