James Brolin says his wife Barbra Streisand becomes a different person when she is in the company of children.

Barbra Streisand

Barbra Streisand

The 78-year-old actor has opened up about the 'Woman in Love' singer's love for her grandchildren and how she "falls apart" whenever she is around little ones and lets any of her "persnickety" house rules go out the window.

He said: "The minute a kid comes into the room, she just changes as a person, she falls apart.

"She is persnickety.

"'Who put those flowers there? You moved that, that's supposed to be on the table right there.'

"The minute a kid comes in, all of that just goes out the window and it's just really fabulous to see somebody disarmed."

The 76-year-old Hollywood legend became a grandmother again to her husband's son Josh Brolin's daughter Westlyn - whom he has with wife Kathryn Boyd - five months ago.

James says his 'Avengers: Endgame' actor son, 51, "dropped everything" to look after his third child and spent "three months" on diaper duty.

He told PEOPLE.com: "He dropped everything. You know how busy he was, for sure, he literally stopped everything and nothing but diapering for three months."

Meanwhile, Josh - who also has 30-year-old son Trevor and 25-year-old daughter Eden with ex-spouse Alice Adair - previously admitted Barbra is an "annoying" grandmother - but in a "really great way".

He said: "My wife got her a bracelet that said 'Grandma' on it and she started crying. She is one of those ... it's annoying but in a really great way, [with] emails every day and like, 'Hey, I thought of this name, what do you think of that? ... When can I come over and feel the baby?'"