When my son was four in England -- Actually, he was four everywhere, to be honest.  If we're being strict about it, wherever he went, he was four that year.
我儿子四岁时在英国-- 实际上他那会儿在哪都四岁 严格地说他四岁那年在哪个国家记不清了， 只记得他四岁那年