An annual report on the troubled authority's child protection service found that the number of children deemed to be at risk of abuse or neglect fell from 1,257 in December 2012 to 806 in December 2013, a reduction of 35 per cent.
In December 2010, the figure stood at 1,408.
The report puts the fall down to shortcomings in the council's information, advice and support service (IASS), which provides a single point of contact for professionals and members of the public who want to raise concerns about a child.
It highlights issues around staff resourcing and inconsistent decisions on whether child protection thresholds have been met.
"A robust action plan and scrutiny are now in place to drive consistency and active intervention to ensure the risks to children and young people are much more robustly assessed and acted upon in the best interests of the child," the report states.
"A direct consequence of more effective practice at the front door will be a more effective response to the needs of children and young people across the city and a subsequent rise in children and young people identified at risk of significant harm."
The report also found that child protection conferences - which take the decision whether to make a child subject to a child protection plan - are plagued by "inconsistent and poor attendance by key agencies", including the police.
It reveals that during 2013, only 77 per cent of initial child protection conferences were held within the prescribed 15-day timescale, compared with 91 per cent in 2012.
The report is an annual assessment of services compiled by the independent reviewing officer.
Birmingham is taking a range of steps to improve performance within children's services.
The department has been rated inadequate since 2009, and has been in the spotlight in recent years over child protection scandals including the case of two-year-old Keanu Williams, who was beaten to death by his mother in 2011, and seven-year-old Khyra Ishaq, who starved to death in 2008.
In December, the council announced plans to work more closely with other agencies responsible for safeguarding children in a bid to improve services.
It also said an additional £10m will be pumped into the service to recruit and retain experienced social workers through initiatives such as benchmarking pay rates across neighbouring authorities, and 'golden hello' payments.
In November, the government ordered a review to decide how children's services should be run at the council.
The review will look at the council's plans for change, whether they are sufficient and what alternatives may be appropriate.