Allergic to new puppy and have to give away

We got a new puppy a week ago, and one of my children is allergic. We have to give the puppy to a friend. How do I coach my children through this so they feel their emotions – don’t suppress — but also don’t take it too hard?? I don’t know how to coach feeling their feelings…bc I don’t know how sad they actually are (we had the puppy for only a week), and I don’t want to try to make them sad just to coach them through it…does that make sense?