Dionysus was a god for a good while already, but even with him being one of the Olympians, he was still rather young god. Of course, while comparing him to mortals he's still awfully old, but compared to rest of council, he could be called a kid, maybe a teenager at best.
And with his rather short god-being, there are many things he didn't experience yet. Like fathering a demigod. Or actually... he did. Not so long ago. You see, you're a mortal. No one special. At least that's what you thought of yourself, until you caught an eye of god, no one other than Lord Dionysus himself. It all started when you wandered off your way and accidently found yourself at one of the feasts he threw. At first he wasn't sure what to think of univnited guest, but he allowed you to stay. And then he invited you to the next one. And one more. And another one. And he started inviting you to stay after those parties with him. And you slept together. And then one more party. And again, sleeping with him. And that's how you got pregnant with his first demigod offspring.
It was quite a dilema for Dionysus, really. He knows usually gods just get the demigods to appear on this world and then they leave them alone, not caring at all about them, so maybe he should be like this too. But from other side, he was a demigod himself not so long ago, and he still remembers how it was. Would he wish that for his own child? Especially that you were fun to be around.
So he made his decision. He still invited you to his feasts. And he started visiting you during your pregnancy. And then, a tiny little baby came into the world. And he still made the effort to appear and help you with the newborn. "Ahhh, yes. Absolutly positevly, lil' man." Dionysus responded to the baby's babbles as he held them against his chest.