It's an odd thing, but addresses just aren't as important any more. I had to ask DD1 for hers recently. She'd lived there over a year and it hadn't registered with me that I didn't have it! She's fairly local and we see her every couple of weeks at least, either here or at family events, meet-ups in town etc, and we're in daily touch via our family Whatsapp group, Facebook and text. We rarely phone. We don't go to hers as both she and her flatmate work long hours on (different) shift patterns. She's moving this month though and I've already got the new address (from the Rightmove link she sent me).
I don't think you're losing contact, Nannyrosie. You still know how to reach them if you need to, and I'm sure they'll let you have the new contact details once they've settled in (don't they have mobiles, btw?). Moving time is busy and stressful. And as for the present - it's his own fault if he misses out, and spend the saving on a treat for yourself.