Melania Trump, the first lady of the United States, briefly stepped out of her husband’s larger than life shadow on Monday to launch a campaign against cyber-bullying – before putting on a show of unity with Donald Trump.

Just as Hillary Clinton was once scrutinized during her husband Bill’s sex scandal, Melania faced the cameras even as Donald Trump kept changing his story about an alleged extramarital encounter with the pornographic film actor Stormy Daniels.

Melania Trump steps out of Donald's shadow – after a year and a half Read more

“As a mother and as first lady, it concerns me that in today’s fast-paced and ever-connected world, children can be less prepared to express or manage their emotions and often times turn to forms of destructive or addictive behaviour such as bullying, drug addiction or even suicide,” Melania told an audience in bright sunshine in the White House Rose Garden, which is normally reserved for events hosted by the president.

“I feel strongly that as adults, we can and should be best at educating our children about the importance of a healthy and balanced life,” she added.

The words were likely to ring hollow with Trump’s many critics. During the 2016 presidential election, Hillary Clinton ran a campaign and ad entitled “Role Models” featuring clips of Trump referring to Mexicans as “rapists” and mocking a disabled reporter. The ad said: “Our children are watching. What example will we set for them?”

But Melania, in her speech on Monday launching the campaign, entitled “Be Best”, continued: “Social media can both positively and negatively affect our children. But too often, it is used in negative ways. When children learn positive online behaviors early on, social media can be used in productive ways. I do believe that children should be both seen and heard, and it is our responsibility as adults to educate and remind them that when they are using their voices – whether verbally or online – they must choose their words wisely and speak with respect and compassion.”

Her husband, however, has become notorious for using Twitter to hurl insults and slap demeaning nicknames on a variety of perceived foes. Sarah Sanders, the White House press secretary, said on Monday: “I think the idea you’re trying to blame cyberbullying on the president is kind of ridiculous.”

Melania also spoke about the need to help children in communities affected by America’s devastating opiods epidemic. After her remarks, she invited her husband to the lectern, as he smiled broadly. He put a hand on her waist and kissed her on the cheeks three times, then told the gathering: “That was a truly beautiful and heartfelt speech. That’s the way she feels, very strong.”

Facebook Twitter Pinterest Melania and Donald Trump in the Rose Garden, where the first lady launched her campaign. Photograph: Win McNamee/Getty Images

Trump said America was “blessed” to have her as first lady. He told her: “Your care and compassion for our nation’s children – and I have to say this and I say it all the time – inspires us all.”

The president then signed a proclamation declaring 7 May as “Be Best Day”. The couple then went back into the White House together.

Guests in the Rose Garden were greeted by a jazz band and included the vice-president Mike Pence, the president’s daughter Ivanka Trump and her husband Jared Kushner.

Slovenian-born Melania, 48, is Trump’s third wife. She was rarely seen in Washington during the first six months of the administration. Her role as first lady to a dramatically divisive president is uniquely challenging.

Anita McBride, the former chief of staff to the ex-first lady Laura Bush, said: “Whenever the president is controversial, it’s sometimes hard to be given credit on your own. You just have to keep plugging away on your own.

The Washington Post reported on Monday that the couple are leading “remarkably separate” daily lives, sleeping in different bedrooms and seldom eating or spending leisure time together. Videos of Melania resisting the president’s attempts to hold her hand have gone viral.

McBride, executive in residence at the department of government at American University in Washington, added: “Only the two of them know what their relationship is like and it’s very hard to lead a personal life in the public eye. It may lead to chatter but it doesn’t seem to be affecting the job she’s doing. God knows, the Clintons had their fair share of troubles on the public stage and they seemed to make it through just fine.”

The Be Best initiatives offer few surprises. Melania had made numerous visits to hospitals and schools and recently turned the blue room at the White House into a mock classroom and invited school pupils to share their aspirations. She pledged to continue with such activities and trips.