Singer Michelle Williams has spoken out in defence of former Destiny's Child bandmate Beyonce's decision not to tame her daughter Blue Ivy's wild hair, insisting cruel critics should focus on their own kids.

Style critics and Internet trolls have taken aim at the Crazy In Love hitmaker and her rapper husband Jay Z in recent months over their choice to let two-year-old Blue Ivy's locks grow out naturally.

The haircare debate even led to a bizarre petition launched online, calling on the baby's superstar parents to comb her afro, but Williams is baffled by the unlikely hot topic.

She tells America's Sister 2 Sister magazine, "Let's worry about your own children and nieces and nephews and make sure they're getting good grades in school and not worry about somebody's hair."

And Williams is warning cyber bullies everywhere not to mess with her or her loved ones.

She says, "I think the cyber bullying is just stupid because the majority of the time most of the cyber bullies just type it (online), but when they see you on the street, they're not gonna say it to your face.

"Every now and then, depending on what day you catch me, if you say something out of line to me - because I don't want you to be ignorant, I want you to be knowledgeable - I will spit something back to you that's factual and I'll say 'God bless you' at the end."

Williams' comments emerge days after Blue Ivy's appearance with her famous parents at the MTV Video Music Awards in Los Angeles on Sunday (24Aug14), when she helped her dad present Beyonce with the Michael Jackson Video Vanguard Award, prompted further haircare criticism from bloggers.

Chris Brown's on/off girlfriend Karrueche Tran also poked fun at the child's hair during a guest hosting stint on U.S. music video chart show 106 & Park on Monday (25Aug14), when she read from a script of jokes and quipped, as Blue Ivy, "I really did wake up like this because my parents never combed my hair."

The backlash she received prompted Bet network boss Stephen G. Hill to apologise for the remark on behalf of his company.