is it possible to leave the child alone or is it necessary to clear the game?
She's necessary to get the harem ending, since obviously she would be a part of it. Otherwise, no you can just woo the other girls and finish the summer off without her, though it's a bit anti-climatic. If you don't want to see most of her, then you can just use the cheats I mentioned earlier.
Everyone keep thinking about
This game here thinking this one the same shit... But no we not fighting off our bros away from giant tittied cows. Worst yet, there's no pregnancy or impregnation endings/gameplay.
Yes, different game. But if you actually play my translation (and I'm a fan of the fetishes you've mentioned and do try to insert them when appropriate in most of my translations), I mention it quite a bit in the game, including the (harem) ending. No, there's no actual pregnancy belly bulges, but use your imagination when reading the text, lol.
Unless you're being sarcastic ... then too bad, haha.