Plentyn Siawns.

[zetlander]

is the Welsh terminology for a child born put of wedlock.

It translates as a 'Child of Chance' which is a far kinder description than 'illegitimate' or the term that  is often seen in Church Parish Registers.

[Jeuel]

I have found a poor lad on the census staying with his grandparents.  His occupation is listed as "bastard".

On the other hand, in my maternal line, I have seen a child on the census recorded as "love child" which is an improvement!  This child's parents later married and she took her father's surname as an adult.

[zetlander]

Another Welsh expression for a child born out of wedlock is 'plentyn llwyn a perth' which translated as child of bush and copse. 
I guess it would be used if the father of the child was not known -- far kinder than some of the English terminologies!

[Hinso]

Perth = hedge

[zetlander]

Perth = hedge

gwrych=hedge