Hi Sarah - have just had a look at the 1891 Census and I would have to say that henry and Rosina are certainly not the parents of Percy!
Henry at 52 is no problem but Rosina at age 54 in 1891 would have been 52 when young Percy was born and I would consider that highly unlikely.
There was also Cordelia who was then age 9 which means Rosina would have been about 45 when she was born.
Quite often when I have found a situation like this I have also found the mother living at home.
It may well be that the mother was not at home on that particular night.
However there is one candidate living at home - Bessie who was then age 23.
Hmmmm - I have now had a look at the 1901 Census!
I would suggest that your initial note about Percy must have been referring to the 1891 Census when young Percy was age 2 and certainly recorded as son of Henry and Rosina.
In 1901 Henry is decased as wife Rose is listed as a widow.
And Percy is here recorded as 'Grandson'.
3 Victoria Place, Penzance
Rose RENFREE, head, wid., 64, St Hilary
Cordelia do., daur., unm., 19, charwoman, Penzance
Percy do., grandson, 12, Penzance
Jane Pryor SINCOCK, visitor, mar., 51, Helston
This 'visitor' might possibly turn out to be a sister but I have not tried to investigate that.
Now - re-thinking my initial comments about Percy being illegitimate and Bessie being the mother.
Bessie does not appear in 1901 although that does not necessarily mean a lot.
It may mean that she had married, was now deceased, or was simply elsewhere.
The other possibility is that percy was the child of a married son.
I have seen instances in the past where a young child was left with it's grandparents while the parents themselves had ventured off to America, Australia etc.
In some cases the parents never returned and the child was brought up from then on by the grandparents.
But the time-period is probably past an era where that likelihood may have been common.
For the moment I am going to stick with Bessie as the possible mother.
CT