Hello Brian
I can't see any children other than Frederick to this couple post 1911 & there isn't an Elizabeth with the 3 other children in 1911 in Warks.
On the face of it,it looks like Charles & Elizabeth were co-habiting & Charles may have deserted the family hence Frederick reverting to his mothers name.There may be other explanations though.
I put a combination of the names Elizabeth,Leslie,Jack & Hilda into 1911 using the "others in the household" box.eg.Hilda Clark with Leslie Clark.
Although there's a couple of hits there aren't any with them together that I can see.
jim