Some children 'may be at increased risk of online harm' during pandemic
It is the largest charity of its kind in the country and helps more than 12,000 children, young people and their families every year.
Ms Janes said: "There are cases of children who have gotten into conversations and situations that are really dangerous.
"When a child is isolated, lonely and vulnerable, they are more likely to talk to someone that you or I would not want coming into the house.
"People don't come into houses through the front door, they come through the telephone line and down a satellite signal, and that is really risky."
The charity helps children and young people who experience the care system, young people who are sexually abused, children who struggle with poor mental health, and refugee or newcomer families.
It has expressed concerns around child protection issues not being identified and referred to the appropriate agencies since schools closed during lockdown.
Ms Janes said the proliferation of new digital platforms for communicating poses challenges.
"People are trying to work from home while monitoring what their children are doing at the same time.
"People need to stay in touch with who their children are talking to.
"Friends used to be someone you went to school with. Friends for our children nowadays are people they meet online."
She said if someone is isolated and vulnerable they are more likely to talk, potentially to the wrong kind of people.
Barnardo's said social distancing measures can exacerbate feelings of loneliness and isolation, leading to chronic loneliness which can impact on long-term mental and physical health and well-being.
Ms Janes added: "We are worried about children and young people and families in all of those areas and we need to think big picture about what happens next and the planning for whenever we exit lockdown or things get back to normal.
"We need to have safe spaces available to them to get the help that they need."
The charity has expressed concern that more families were being pulled into poverty due to job losses or increased financial pressures.
It said child protection must be prioritised and mental health support and access to counselling should continue after the pandemic.
It also urged extra help for families affected by poverty due to the economic crisis and warned the pandemic threatened the existence of charities.
"Funding security, including longer-term commissioning, is needed to ensure the vital services delivered by the third sector can continue to address the legacy of the pandemic in years to come."