Goblins are small, black-hearted humanoids that lair in despoiled dungeons and other dismal settings.

This is from D&D Beyond.

All sources say their alignment is Neutral Evil.

FR wiki's explanation for their evil alignment is: "goblins often had a short temper,[7] and were more easily provoked than individuals of most other races.They often found it difficult to overcome this short fuse, and had a sense of greed that made it difficult for them to act altruistically.They also generally took sadistic pleasure in exacting revenge once crossed."

So, their very nature drives them with desires towards evil, making them, in general, an evil race. Are their exceptions? Yes. But the goblins in BG3 are obviously not the exceptions. They are evil, for they are killing and eating people. Their kids are partaking in the killing and eating of people. Therefore, they are all evil.