Dear, darling Sebastian,
What a brave boy you are! Daddy says you got on the train and climbed out the back into the tunnel, just like we practiced. We were so worried when we saw the train pull away! What if the windows had been locked? It was agony waiting to know you were safe.
Daddy says you're cross with him for not coming earlier, but please understand. It's too risky, except on days when he can "inspect the tracks".
Daddy will bring you food every Tuesday. Try to make it last. We don't have ration coupons for you anymore, but that's all right, as I need to reduce anyway.
Courage, my little soldier!
P.S. I've asked Daddy to smuggle Aloysius to you. I know you think you're too big to sleep with a teddy bear, but it's good to have a comfort of home, no?