The money will be available to a total of 20 councils - representing less than one in seven top-tier local authorities - which will share £85m over the next five years. That works out at an average of an extra £850,000 a year for each authority if the money is allocated equally.
But which local authorities can expect to see the money? Hammond says it will go to councils "with high or rising numbers of children in care". But precisely how this will be calculated is unclear.
Based on the most recent looked-after children statistics available, the league of councils with the highest overall numbers of children in care is topped, perhaps unsurprisingly, by Kent, with 1,900, driven partly by its status as the main entry point for unaccompanied asylum-seeking children.
It has already received additional support as part of £20m provided to councils supporting child refugees, and the number of children it looks after actually fell between 2016 and 2017 by 415 as a result of efforts to accommodate unaccompanied children in other areas. However, earlier this year the council warned that as a result of remaining responsible for child refugees once they have turned 18, their care leaver budget is underfunded to the tune of £4m.
Bradford was found to be inadequate by Ofsted earlier this week. Croydon, Surrey, Wirral and Worcestershire are all also currently rated "inadequate"
Meanwhile, Lancashire is recovering from serious problems and, until a reinspection of provision published in August, was also deemed to be "inadequate'.
Norfolk, and Northamptonshire - which is struggling to such a degree financially that emergency spending limits have been imposed twice this year - have both recently been upgrade from "inadequate" to requires improvement.
Of the other areas to appear in the top 20 - Durham is also rated requires improvement, while a total of eight councils - Essex, Kent, Hampshire, Hertfordshire, Leeds, Nottinghamshire, Staffordshire and Suffolk - are all currently rated "good".
Only two of the authorities with highest overall numbers of children in care appear in the top 20 for those showing the largest percentage increase in care numbers in the year up to March 2017 - Durham and Wirral.
That table is led by Telford and Wrekin, which saw numbers of children in care rise by 26.7 per cent between 2016 and 2017, from 300 to 380. Three other councils experienced rises of more than 20 per cent. Hartlepool's care population grew by 24.4 per cent, from 205 to 255, Windsor and Maidenhead's by 22.2 per cent, from 90 to 110, and Durham, by 20.7 per cent, from 675 to 815.
The picture is further complicated by some councils having higher proportions of their local child populations in care. The highest rate is Blackpool, with 184 children in care for every 10,000 children, Hartlepool with 129, and Hull with 124. In total there are 15 local authorities with a rate of 100 or more children in care per 10,000 of the child population. The national average in 2017 was 62.
However, this could all change when the latest figures for numbers of children in care, as of March 2018, are released. They had been due to be published in September, but the DfE has said that this year they will be published two months behind schedule - in November. The DfE did not provide CYP Now with a reason for the delay.
Hammond said the money would be used to "expand our successful social care programmes" - which could indicate a roll-out of initiatives already tested as part of the DfE's Children's Social Care Innovation Programme, which has investment of £200m for the six-year period to 2020, and has so far supported a total of 98 projects.
A study into the first wave of initiatives funded through the programme, which launched in 2014, found that 24 of 45 projects evaluated were succeeding in lowering numbers of children coming into care.
Initiatives funded through the scheme include the Pause project, which aims to break the cycle of repeat pregnancies among women who have already had a child taken into care, and has already been extended to nearly 20 councils in England, as well as Northern Ireland, Scotland, and Wales.
Hammond also announced a further £410m in 2019/20 for both adult and children's social care, but didn't give any detail on how this will be apportioned.
But children's services leaders have warned that the additional funding will not be enough to address pressures on services.
"We are becoming increasingly concerned at the government's piecemeal approach to funding children's services," said Stuart Gallimore, president of the Association of Directors of Children's Services.
"Ad hoc, time-limited pots of funding for some local areas and not others falls woefully short of the sustainable and equitable long-term investment in children and young people that is required to ensure high-quality, safe services are available for them at the earliest opportunity."
"The Chancellor announced £410m for social care in 2019/20, with no further detail about how this will be shared or allocated. Whilst any additional funding is to be welcomed, we need five times this amount just to plug the funding gap expected in children's services by 2020."