You need to check the GRO indexes for his marriage. This can be done online at
http://freebmd.org.uk/cgi/search.pl.
It was in 1900 in St Ives registration district, in which Fenstanton is situated.
It's difficult to trace any children with a common name like Young, particularly as you don't know how long they stayed in Fenstantion. You can check the GRO birth index for Young births in St Ives registration district, there are two that look promising in 1901 and 1907. But you have to buy them to find out if they are children of Evelyn and Amy. And FreeBMD births are complete only up to about 1912.
Fenstanton has a good website at
http://www.ti0.com/fenstanton/Looking at the Kelly's 1918 directory link on the site it appears that the Rev Young was no longer there in 1914.
In the genealogy section on the site you can register to get the master index of BMD entries, which is probably what you need.
In 1891 he was living at Back St, Harlow Essex, Evelyn Young, lodger single 24 Mathematical master of St Mary's college and curate of St Johns, born S. Milford Yorks, so he'd obviously left home by then
There are transcripts of marriages in various Cambs parishes on Ancestry.com which were done by the Rev Evelyn Young, but unfortunately there's no further detail as to when they were extracted or for which parish he was rector.
Googling "Rev Evelyn Young" will help you in putting together his movements after 1901 - eg he was vicar of Toft Cambs 1914-21 and another hit gives his death as 1936. Genealogists have a lot to thank him for as it appears as though he transcribed most of the marriages in Cambs, which were used as the basis of the Cambs entries in Boyds marriage Index
The only death in 1936 which fits is that of Evelyn Young age 69 in Bingham registration district in the June quarter 1936 vol 7b page 500. You need to order the certificate from the GRO, cost £7, to get more details
David