Solange, who used to be married to Daniel Smith, said that the singer is very "hands-on" and trustworthy.
She told OK magazine: "Beyoncé's very hands-on. I've had two weekends where I've been able to hand him over, and it's been very nerve-racking for me, but she does a great job."
Talking about Beyoncé and her husband Jay-Z, Solange added: "They actually request him more than I'm willing to give him. But the bedtimes we got to work on. Sometimes I'll call expecting him to be asleep, but he's still up!"
Solange described the rapper as a "very good uncle" and "pretty cool".