Should I offer a refund?

[RisingDamp]

Hi there,
I run a very small holiday accommodation business at our home. A family booked in on a cheap last minute deal for a week and after three days they have said one of their kids is ill (high temperature) and they are going home early.
They are asking if they can come back again for a weekend later in the year for free "as they have had such a lovely time and are so sorry to be missing out" etc.
I'm torn. On the one hand I want to create a good vibe, on the other, it's too late to let these unexpected spare nights this week to anyone else. Also, weekends later in the summer are our popular time, when I make my money...
From where I stand, I'm amazed they have asked this but am I being unreasonable - what would you do?
Suggestions?

Don't offer.
I have been in a situation where we cut our holiday short when DS2 became sick.
Unfortunate for us but one of those things that happen.

Would never have occured to me to ask to come back later.

I'm really sorry your child is ill, but as it is your choice to leave early, I'm unable to offer you a refund or discount. Do you have a Terms & Conditions they may have agreed to?

We left one holiday early 'cos it rained and rained and rained and it never occurred to us just to write the cost off. Damn, I should have asked for money back for bad weather!

Word of mouth is excellent for business. I would offer a small discount on a future booking but make it clear this is really going out of your way.

If it was your fault their child got ill then yes, otherwise WTF?!