I found them on the 1851 cenusus
HO107/2186/115/27
Cooper St Toxteth Park
Thomas Head M 28 Labourer Liverpool, Lancs
Sarah Wife M 29 Liverpool, Lancs
William Son 4 Scholar Liverpool, Lancs
I couldn't find a marriage for them though. I had a look on the 1841 census and I think and I do mean think there maybe one possibility.
HO107/124/7 Folio4 Page 3
Neston, Wirral
Joseph Youds 35

born in county
Catherine 35 born in county
Sarah 15 not born in county
the enumerator has stuck to his brief everyone over 15 has been rounded down to the nearest 5 or 0 on this page.
There was I noticed a marriage of a Sarah Youds on the Wirral but definately not to anyone with the surname Wright. so I may be leading you up the garden path.
I tried to find them on the 1861, but there are loads of William/Thomas Wrights in Lancashire
Libby
William 8 born in county
Ellen 4 born in county