Kids understand love. What they don't understand is deception or hiding. And it's never too late to come out to your child . I know folks in their forties whose parents are just now coming out to them. A lot of mysteries are being solved, and missing puzzle pieces falling into place for these families, and it's a good thing.
Kids go through stages.
You don't need me to tell you that. They'll accept you much more quickly with that basis of support. And, conversely, just cause your kid is doing fine now, doesn't see that the big deal is, etc. Introduce them to other kids with gay parents. Make positive books available.