When i was younger i always wanted a penpal and as i have grown up i realised i still love writing letters and postcards and making someone smile with my little bit of post
I recently found out about a charity called PostPals which have a website featuring children which severe or termainal illnesses who love to receive mail. You can read a bit about each child and see what they like and then send a little card or letter to them to make their day brighter! The website is www.postpals.co.uk/
You could get you kids to start a letter and add to it every time they do something exciting over the holidays and then post it to one of the children to tell them about their adventures.
Or even try and pick up some little gifts whilst you are out and about over summer. You could decide on a child beforehand and set you children on a mission to find a few bits they think that child might like, and then put a little package together and sent it.
Anything from a souvenir from your holiday, an extra item when you go shopping or a postcard from the beach - All of these wil make one of the children smile, and give your kids a different activity to do when they undoubtedly get bored!