* Residents allowed back 3 years after disaster
* Families split; fears over radiation impact on kids
* Mayor calls return 'a fresh start' (Recasts with returnees, changes date in dateline)
By Mari Saito
TAMURA, Japan, April 1 (Reuters) - People in Japan on Tuesday began their first homecomings in three years to a small area evacuated after the Fukushima disaster, but families are ...