A good spot indeed!
Ian I H S. and Laura HEYBROOK are parents of the following according to the GRO indices
Henry, b Q2 2002 Kensington & Chelsea (as above)
Frederick (Freddie) T V S., b Q1 2009 Oxfordshire
Violet I R S., b Q3 2010 Oxfordshire
Based on the convention of listing grandchildren in age order, this means Anna and Alexander born between 2002 and 2009, and presumably are James' children? I'm not able to identify a good candidate marriage for James in the Ancestry indices to 2005. There are no GRO marriage indices yet.
There is only one Anna in this timeframe:
Anna F S., b Q1 2004 Truro
However, we should acknowledge the possibility of a different surname.
There is no obvious candidate for Alexander amongst several possibilities - I also checked for Thomas Alexander in case that convention was being continued.