At least 15 people were killed and another 42 injured in the shooting that targeted a Hanukkah festival, in the nation's deadliest massacre since Port Arthur in 1996.
The attack, footage of which has been widely broadcast and shared on social media, was allegedly carried out by Naveed Akram, 24, and his 50-year-old father Sajid Akram.
Naveed Akram was critically injured and placed under guard in hospital, while his father was killed in a shootout with police.
Mental health charity Smiling Mind expects a surge in demand from Australians in coming days, especially from parents seeking advice on safeguarding the wellbeing of children.
CEO Sarah La Roche urged parents to limit their kids' exposure to footage of the incident and to talk about their feelings.
"It's important to reassure children that they are safe and that they are within the safety of their parents," Ms La Roche told AAP.
"We also suggest not averting a conversation all together but creating space to talk and inviting questions so that they feel supported with their worries."
It was important parents responded honestly to children about what occurred "but in an age appropriate way", she said.
"Try to limit the complexity of what you're sharing so think about factual explanations and focus on what's known."
Hundreds of locals, tourists and those attending the Chanukah by the Sea festival fled from Bondi Beach when gunfire erupted on Sunday evening, with many witnessing the carnage.
For those in the Bondi Beach area, the NSW government is setting up local mental health support over coming days and weeks.
Beyond Blue, another mental health charity, cautioned that the massacre, like other violence and acts of terror, could bring with feelings of shock, grief, profound sadness, anger and fear.
It urged people to be on the lookout for feelings of overwhelm, numbness or detachment as well as difficulties focusing or planning ahead.
Other worrying signs included irritation, being constantly tearful or mentally replaying the event multiple times, it said.
It was "normal to experience these emotions while trying to make sense of distressing events".
"Give yourself permission to feel what you're feeling, take care of your body and mind with rest, healthy routines and relaxation, and reach out for support if you need it," CEO Georgie Harman said in a statement.
"Children look to adults to learn how to respond - be mindful of your own reactions near them.
"Encourage questions and explain it's normal to feel scared or worried and remind them they are safe."
Lifeline 13 11 14
beyondblue 1300 22 4636
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