The Duke and Duchess of Cambridge visited the YoungMinds Parents Helpline headquarters in Southwark on Thursday as part of their Heads Together campaign.
YoungMinds is a charity which works to improve the emotional wellbeing and mental health of children and young people.
The Parents Helpline is a free support network to advise parents who are concerned about their child. The helpline can assist with behavioural and emotional issues as well as mental health.
After chatting with staff and volunteers, the Duke and Duchess took part in a short course in becoming a helpline volunteer.
Prince William said: "I found it very eye-opening. I thought the service was fantastic.
"I think it's fantastic, the idea that you've got these very caring, lovely people on the end of the phone who listen for as long as they need to, to build the picture of what is going on, and then provide extremely good advice – and then the fact that you've got the mental health professionals later down the line if necessary.
"I think that is a really good Balance of getting the right support straight to these families who are clearly at their wits' end at what to do, and reaching out. Thank goodness they do reach out to something like this."
The Duchess said: "What we've taken away is just how normal it is. We are parents ourselves, I am sure we will face worries – we do face worries, because we've got small young children. I
"f those worries escalate, how vital it is to get support – and you are providing that support.
"As a parent and as a mother, having that feeling that there is somebody there that is non-judgemental, that can provide the professional support, and that can really provide a helping hand at a really difficult time, makes a real difference.
Prince William added: "It is important that parents understand that you can't be brilliant at everything. It's totally fine to talk about it and to seek help and to speak out, because we're not all superheroes.
"There is a lot of pressure on parents, and most of it is self-made by parents themselves, where you feel you have to be able to handle everything. You have to show strength and resilience to everything. But there are some times when it all gets too much and you need to reach out."
Heads Together is a mental health campaign led by The Royal Foundation in partnership with YoungMinds and seven other charities. The aim of the campaign is to challenge mental health stigma and change the national conversation on mental wellbeing.