Union - who has Kaavia, 18 months, with her husband Dwyane Wade, and is also stepmother to his children Zaire, 18, Zaya, 12, and Xavier, 6 - said: "For me, it's the bathroom. Thank god they respect the toilet. I go in there, I claim gastrointestinal issues. No one will ask follow-up questions about that. And then I milk it, sometimes for 20, 30, 45 minutes.
"I can just play words with friends. I can just mindlessly scroll social media. But it just gives me a minute. I can go in the bathroom, lock the door and sit down."
Alba doesn't have the same luck, though, as her children will FaceTime her as soon as she's out of sight.
Speaking in a joint interview with Union for E! News, she joked: "My kids FaceTime me all day long. They get into arguments, and they each FaceTime me their version of the argument. And I'm like, 'Why are you bothering me? I don't care. I just don't care.'"