And Tango Makes Three by Justin Richardson and Peter Parnell

Roy and Silo are just like the other penguin couples at the zoo - they bow to each other, walk together and swim together. But Roy and Silo are a little bit different - they're both boys.

Then, one day, when Mr Gramzay the zookeeper finds them trying to hatch a stone, he realises that it may be time for Roy and Silo to become parents for real.
 
And Tango Makes Three with illustrations by Henry Cole.