Frequent crying in children is not normal and could be a sign the child is depressed, says Dr Anthea Rhodes from the Royal Children's Hospital.

Primary aged children can suffer depression yet many parents struggle to spot the signs of a mental health problem in their children, a national poll has found.

Research released from The Royal Children's Hospital's Child Health Poll found only a third (35 per cent) of more than 2000 parents surveyed were 'confident' in recognising the signs of a mental health problem in their child.

A further third of parents believed a child's mental health problems might be best left alone to work themselves out over time; and less than half (44 per cent) felt confident they would know where to get help if their child experienced social, emotional or behavioural difficulties.

Director of the RCH Poll, paediatrician Dr Anthea Rhodes says children can develop many of the same mental health difficulties as adults but they often manifest in different ways, making them harder to recognise.

Frequent tearfulness and crying is not normal in children and seeking professional help sooner rather the later is really important, Dr Rhodes says.

Ongoing physical complaints can also be a sign of social or emotional problems in children and teenagers.

"Even if parents are unsure, there is no harm in having a conversation with their GP or school counsellor about any emotional, social or behavioural difficulties they think their child may be experiencing," Dr Rhodes added.

"Ignoring signs that may indicate a child is in need of help can result in the problem becoming more entrenched and much harder to treat."