Kieran Culkin Expecting 3rd Child With Wife Months After Oscars Bet Reveal

Kieran Culkin finally got his wife to hold up her end of their bargain ... 'cause his better half's pregnant, months after he revealed she promised him four kids if he won an Oscar!

The actor rolled up to opening night of "Waiting For Godot" on Broadway with Jazz Charton -- his wife of more than a decade -- and, he put his hand protectively on her belly ... and she's clearly with child!

The two are positively beaming in the photos ... with Culkin looking particularly proud of himself -- since he sorta manifested this whole situation.

Remember ... during the 97th Academy Awards back in March, Culkin won Best Supporting Actor for his role in "A Real Pain" ... and, he told a story about how he'd mentioned to Jess he wanted two more children.

Jokingly, Jess told him she'd give him two more kids when he won an Oscar ... and, he ended his speech by telling her they should probably "get cracking" on making a couple more little Culkins.

Charton was clearly shaking her head and mouthing an unmistakable "No" ... but, it seems she wasn't too averse to having another baby in real life.