EXCERPTS
Welsh councils also lag behind those in England and Scotland in having enough holiday childcare, the Family and Childcare Trust said.
The trust claims finding decent, affordable care for school-age children is "down to luck" for many families.
A Welsh government spokesman said it was committed to improving access to affordable childcare.
The trust drew on its own surveys, a poll of parents and an analysis of councils' own assessments of the supply and demand for childcare in its areas for the study.
The analysis concluded that two fifths (40%) of councils across England, Scotland and Wales had enough out-of-school care for five to 11-year-olds during term time in all or most local authority areas.
The figure for out-of-school activities for 12 to 14-year-olds in all or most authorities was one in four (25%) across all three nations.
But when that figure was broken down by nation, the finding was 27% in England, 28% in Scotland and 5% in Wales.
Wales was also the lowest of the three countries on the provision of enough holiday childcare at 18%.
The report said: "For many families whether they find affordable and quality childcare is down to luck.
"The current out-of-school childcare system has serious problems when it comes to availability and affordability and in many areas not enough is being done to make things better.
"Out-of-school childcare needs to be given greater attention by government and local authorities."
Read online at BBC News