I've just lost all the info I posted! (dodgy wireless connection- will save before I try posting again!)
Free BMD has birth for Herbert Maddock 1891 Peterborough district (Crowland is just outside here according to map)
There is also one for Eliza Limming 1896 Bourne.
However I can't find either of them in 1901 census

If all else fails I think it would be worth getting the Phyllis Mattock birth certificate -just to eliminate. The birth cert of one of other children would give an indication re status of Herbert and Eliza.