Spouse has FSHD, an inheritable muscular dystrophy. Should we have our toddler tested?

My spouse was recently diagnosed with FSHD, which is an autosomal dominant inherited form of muscular dystrophy. We are currently awaiting genetic verification but are wondering if we should have our toddler tested if my spouses' test comes back positive. There is no family history for it but it is known that about 1/3 of these cases are spontaneous mutations.

My spouse is only affected relatively mildly so far (foot drop on one side, minor facial muscle weakness, general but still minor muscle weakness), which is encouraging, especially given that we are already in our 40s. Although the current diagnosis is preliminary, her symptoms are a perfect fit for this disease. Our child appears to be physically fine but it may just simply be too early to tell. There is currently no treatment.

Obviously, it seems pointless (if not dangerous; think "pre-existing condition") from a pure practical standpoint to try to find out if a person has a disease before it manifests itself if there is no therapy available. However, the emotional and psychological considerations are difficult for us to work through right now. Eventually, my older kids from a prior marriage will want to know more details and it will be hard to keep those a secret from our child. I am also not sure about any future ramifications of keeping those kinds of secrets even if it was possible...