A row has broken out about the choice of a recital poem for children at this year's Urdd Eisteddfod in Cardiff.
Myrddin ap Dafydd, composed the poem five years ago
A head teacher has said the poem "Chei di ddim odli" (There Shall Be No Rhymers) by Myrddin ap Dafydd is unsuitable for children under 12.
A union has received complaints from schools and parents about the poem containing irreverent words like "bum".
But the poet said the work should be put into context by teachers and have the background explained to them.
Ann Williams, head teacher of a Cardiff primary school, Ysgol y Mynydd Bychan said she would not be teaching the Welsh language poem to her pupils.
"Parts of the poem are quite vulgar. I don't agree at all that children aged 10 or 11 should learn to recite vulgar words.
"Children ask what these words mean.
"Many of the children attending the school are learning Welsh and we have to translate this into English and explain what it means," Ms Williams added.
The poem was commissioned in 2000 and written by the then Welsh children's poet laureate, Myrddin ap Dafydd from Llanrwst, who is also a chaired bard.
"Chei di ddim odli" refers to wide ranging laws in the Middle Ages which banned the Welsh from owning land and from carrying arms for example.
"I would ask everybody who introduces the poem to children to put it into context and explain the history behind the poem," said Mr ap Dafydd, who owns the publish company Gwasg Carreg Gwalch.
"The story refers to the era of Owain Glyndwr.
"The Welsh had been oppressed and this is the key to the poem - you can't rhyme, can't sing and you can't protest against the oppression.
"The poem is an anti-racist one and the background needs to be explained to children."
Rhys Williams from the National Union of Teachers in Wales said he sympathised with teachers from Cardiff and the Vale area who were unhappy.
"I think it is a brilliant poem, I think it's satirical and I think it's exciting," Mr Williams said.
The Director of the Urdd Eisteddfod, Siān Eirian, has defended the poem
"But I do sympathise with the teachers who phone us and say its not suitable for nine and 10-year-olds."
Mr Williams said the Urdd had to be careful as it was expected to be an inclusive movement.
"A lot of people feel if you speak Welsh you buy up the whole package - the politics and everything - but it's not necessary."
Director of the Urdd Eisteddfod, Siān Eirian, defended the poem, which had been chosen by a recital panel for competitions in May.
She said it "introduced a piece of Welsh history in a satirical and funny way" and had been written in a "tongue in cheek manner."
"I've listened to the criticisms and I've spoken to experienced recital teachers and they're more than happy to teach the poem to their children," said Ms Eirian.
Meanwhile, teachers at Cardiff's Fitzalan High School have told BBC Wales they will be withdrawing from all competitions at this year's Urdd National Eisteddfod in Cardiff as a result of another poem - called Bwyd Od (Odd food).
They claim it borders on racism, but Ms Eirian said it had been misinterpreted and that not of the recital competitions would be changed.