Being enrolled in school is not mandatory. The law states that children must receive an education in "school or otherwise". So if you don't want to enrol him just yet, then you can wait.
(Just in case you wanted the actual law -
Section 7 of the Education Act 1996, applying to England & Wales:
"The parent of every child of compulsory school age shall cause him to receive efficient full-time education suitable—
a: to his age, ability and aptitude, and
b: to any special educational needs he may have,
either by regular attendance at school or otherwise.")
Life is education otherwise, and surely moving countries is enough of a life-learning experience to wait to enrol in school whenever you and your child feel ready to do it!
And if he isn't enrolled, they don't even need to know he isn't going.