Parents have said they face "unfair" charges as several councils ask for donations for breakfast clubs which the Welsh Government said should be free.
Primary school children in Wales are entitled to a free breakfast, but six councils apply some charges to parents.
Carmarthenshire council has just started asking parents for a £1 donation in a bid to raise £50,000.
The Welsh Government said "on no account" could any costs be applied to any aspects of free breakfast clubs.
The policy was announced in 2004 and local authorities are required to provide free breakfasts to schools should they ask for it - the scheme covers 30 minutes before school, should they sign up.
There is no legal requirement on a governing body to provide free breakfasts and schools who do not take part in the Welsh Government scheme can run separate breakfast clubs.
Gwynedd, Monmouthshire and Wrexham councils all charge for childcare between one hour and half an hour before the start of breakfast clubs, while Powys and Ceredigion councils said the same charges could be applied and vary between schools.
Carmarthenshire council said 96 schools were signed up to the scheme - only four do not take part - but one parent said the voluntary donation request was "unfair".
Amanda Osborne-Yip, whose children use the breakfast clubs at Ysgol Dewi Sant in Llanelli, said: "If they've said it's free, then parents rely on it and they should stick to their word.
"Some parents won't be able to afford it and it's important that children have something healthy to eat before starting their school day."
Another parent, Ryan Greaney, said he did not mind contributing but said it could affect some parents.
"It's been free for such a long time I think people would make a fuss if they were asked to make contributions," he said.
"If they said it should be free they should be honouring that."
Heulwen Jones said she had no problem donating £1 if it went into other services, adding: "Personally I don't mind that we have to pay. It's a valuable service for us as parents, especially working parents."
Ysgol Dewi Sant head teacher, Ann Clwyd Davies, said: "The decision was made and the policy was written many years ago and I think many pupils now make use of the clubs, so they just need to relook and be clear as regards the criteria of children who receive the club for free and those who make a financial contribution."
A Carmarthenshire council spokesperson said: "To support the viability of the breakfast club service in schools, parents or guardians can make a voluntary contribution towards the running of the breakfast service.
"This will contribute towards the cost of the appropriate supervision required - suggested at £1 per family per day."
Elsewhere in the UK, the Scottish government said local authorities could provide free breakfasts as part of their funding allocations, while the UK government and two charities launched a scheme to provide free breakfasts to children in 1,770 primary schools in deprived areas of England last year.
The Welsh Government said: "Free school breakfasts are just that - free. On no account can a school apply any costs to children and their families for any element of the free breakfast session."
Do schools charge where you live?
- Anglesey - No charge
- Blaenau Gwent - No charge
- Bridgend - No charge, but one school does not have a breakfast club
- Caerphilly - No charge, but one school does not have a breakfast club
- Cardiff - Schools can charge for additional provisions alongside a free breakfast
- Carmarthenshire - Voluntary charge of £1 for care before the free breakfast clubs
- Ceredigion - Schools may charge for care prior to the breakfast club
- Conwy - No charge
- Denbighshire - Did not respond
- Flintshire - Schools may charge for care if the breakfast club is longer than 30 minutes
- Gwynedd - Charges £1 for pre-school care clubs which run before the free breakfast clubs
- Merthyr Tydfil - No charge
- Monmouthshire - Charges £1 for care before free breakfast clubs. Clubs are free for pupils entitled to free school meals
- Neath Port Talbot - No charge
- Newport - No charge
- Pembrokeshire - No charge
- Powys - Some schools do charge for breakfast club provision, which varies between schools
- Rhondda Cynon Taf - No charge
- Swansea - Did not respond
- Torfaen - Did not respond
- Vale of Glamorgan - No charges for schools in the scheme, but other schools may charge at their discretion
- Wrexham - Charges £1 for care before the free breakfast clubs. Clubs are free for pupils entitled to free school meals