The two charities began negotiating on Friday last week, four months after the Children's Society announced it would be pulling out of Wales.
Subject to further talks, the Children's Society will form a temporary subsidiary within Children in Wales with its own project board from August.
All but two of the Children's Society projects will continue under the auspices of Children in Wales. The Church in Wales will take on the other two.
Catriona Williams, chief executive of Children in Wales, said: "This is to give time and space to get a long-term solution. Children in Wales will not be the long-term host."