There's a couple with a three-year-old and a persian cat living in our street...it was quite an old cat and this cat went missing several weeks ago...as you know some cats chose to be on their own when it's time to leave for RB and Simba was such a cat...he was well loved and the child absolutely loved him to pieces...the whole family was devasted about the death of the cat and the way he has chosen to leave and not knowing how to tell a three-year-old about the death they've told her that Simba has left for his relatives in Africa...however this cat had a wonderful home and was well cared for...
I live in quite a small town (population 55,000) and here are areas where I think it's not appropriate to let a cat outside, but we live on the outskirt and it's quite a safe place and all neighbor's cats are quite old...
What I want to say is, that maybe the family who applied for the kitten isn't that bad and maybe they can offer the kitten a wonderful home...your kittens are six weeks now and it is still some time before they'll go to new homes, maybe if you'll visit their home before and get an impression about the family (let them show you pics of their old cat etc)...and listen to your gut feeling then...
I didn't mean to offend you, but a personal impression can give you more than just having been told something about this family...
If you then feel they're not the proper family you can still look for other options...

Wishing you all the best with placing the little kittens into loving homes!!!
And again I didn't mean to offend you with telling you this, it's just another point of view...