According to Children and Family Court Advisory and Support Service (Cafcass), the number of open cases at a given point in October was 30,256.
This is a rise of 7.3 per cent on October 2018's figure of 28,202, which was an increase of 11.9 per cent on the previous year.
These cases require more legal work before they can be given an appropriate disposal.
Cafcass recently reported receiving 5.8 per cent fewer new care applications in September 2019 compared to the same month the previous year.
But the service's chief executive Jacky Tiotto said it is still operating "at peak capacity", and she believes that caseload level offers a more accurate measure of this than numbers of new applications.
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The President of the Family Division is looking into how cases can be dealt with more effectively and has recently completed a consultation on plans for future reform, with the results yet to be published.
In its consultation response, the Association of Directors of Children's Services says that cuts to funding is a key challenge courts are facing in tackling cases.
It is calling on the government to ensure there is further investment to reduce backlogs in the system and to help councils avert the need for court involvement.
"Put simply, if there are more children and families encountering the courts, fewer judges and support staff and indeed fewer court buildings, then performance will understandably be impacted," states the ADCS response.
The association suggests that the complexity of cases that reach courts is another factor in the backlog.
"In taking a whole-system view of activity, it's worth noting that for every case brought before the courts, local authorities are working with dozens of others to safely manage risk in the community in a bid keep families together (where this is in the child's best interests).
"It is therefore inevitable that the cases that do come before the courts are the riskiest and most challenging," the ADCS's response adds.
Reducing the use of independent social work experts in court is among proposed reforms that the ADCS is backing.
Their use "adds delay", it claims.
"It is not always clear what value independent social workers, who do not have an established relationship with the child, can add, although there are clearly come exceptions - for example, the provision of specialist advice in relation to international assessments.
"Again, there is significant variation in usage of expert witnesses across the country.
"ADCS appreciates that family court judges face very difficult decisions where the evidence is frequently in the balance between different disposals, further expert opinion can be sought in the hope this will ease the decision-making process, but often it does not," states the ADCS.
It believes no individual body can bring about the much-needed transformation and recommends a "partnership of leadership" takes a plan forward.
It adds: "ADCS members are committed to working alongside the president of the Family Division, relevant government departments, Cafcass and other representative groups to bring forward a clear narrative and vision to knit together the myriad relevant workstreams, reviews and programmes in this area in order to improve children's outcomes."
