Is it possible that a child could inherit his parents' diabetes even though the parents doesn't have diabetes yet when the child was born?

Diabetes: Yes its possible that at some point in its life that child can develop diabetes, since it can be a genetic condition. Doesn't matter when the parent gets it.

Low risk in general: There are increases in risk based on genetic factors, but someone who got it as a kid is not necessarily going to pas that on.Probably 5% risk for Type 1 DM in their kids. Type 2 is likely higher, but the genetic influences are aided by the tendency of older adults to put on excess weight,which adds to but is not the sole factor in its development.