I think that in this context, 'fairy child' probably is meant as a compliment. If you're looking for lyrics of songs in Irish or in Scots Gaelic there's the website -
http://www.celticlyricscorner.net where among others you can find the lovely-looking Méav -
http://www.celticlyricscorner.net/meav/index.htm. In fact it's quite common nowadays to have the lyrics and their translations provided on the sleeve notes of CDs recorded by Irish and Scots Gaelic singers and musicians.
This is in the sleeve notes of 'Suantraí' recorded by Pádraigín Ní Uallacháin -
Children were prey to abduction by the fairies especially male children because of the traditional idea that the male gives more of its characteristics to offspring and therefore more human blood to the fairy race. This emphasis on abduction reflects the function of fairies as a means of warning children to stay near home. The early death of a child was often seen as an abduction by the fairies......
Mullach a' tSí
Ar Mhullach a' tSí tá síoga geala
Fá chaoin ré an earraigh ag imirt 's ag spóirt
Seo iad aniar chun glaiogh ar mo leanbh
Le mian é a tharraing isteach sa Lios Mór.
Uiseó uiseó uiseó mo leanbh uiseó mo leanbh uiseó a stór
Uiseó uiseó uiseó mo leanbh uiseó ní imeoidh tú leo.
Goirm thú a chroí ní bhfaighfidh siad do mheallach
Le brí a gcleas ná le binneas a gceol
Tá mise led' thaobh ag guí ort 's ag beannacht
Seothín a leanbh ní imeoidh tú leo.
Seoithín seothó mo stóirín mo leanbh
Mo sheod gan cealg mo chuid den tsaol mhór
Seoithín seothó nach mór é an taitneamh
Mo stóirín 'na leaba 'na chodhladh gan brón.
The Fairy Mound
Above the fairy mound there are bright fairies
Playing in the soft light of the spring moon
Here they come to call my child
With desire to entice him into their ringfort.
Lulla lulla lulla my child lulla lulla lulla my love (treasure)
Lulla lulla lulla my child lulla mychild you'll not go with them
My darling my own they will not entice you
With the strength of their tricks or the sweetness of their music
I'm by your side praying and blessing you
Lulla my child you'll not go with them.
Lulla lullo my little love my child
My jewel without blemish my only one
Lulla lullo great is my pleasure
My little love (in his bed) asleep without sorrow.
A changeling in Irish is :
http://www.teanglann.ie/ga/eid/changeling