We don't really worry about it. They're DH's relatives and after a couple of years of trying we decided we strongly dislike them. So we see them once or twice a year and don't worry about the other time in between.

Weekly Skype/Facetime.
Sharing photos or short videos via text.

And, just talk to your kids about them a lot. Talk about memories of things they’ve done with those relatives on visits, things those relatives have shared with you, etc.

WhatsApp for sending pictures and making video calls, and yearly visits.

We talk everyday or every other day on the phone, we video chat, and text frequently. I do this with friends and family in another country. We visit several times a year, and they also fly in to visit us, too.

My family is scattered around the world. We use WhatsApp to stay connected.

Grandparents in another country - I email back and forth a few times a week and we try to do a weekly Skype.

If you have relatives who live far away, what do you do, or do they do to keep connected with your kids?