I must confess that at first I was really puzzled by this question. Growing up in Oz in the 1950s and 60s Valentines Day was mostly unrecognised and seen as a rather sentimental "American" thing. When it started to become more mainstream (or more commercialised) over the last 20 or 30 years it only applied to lovers, whatever their actual status. My first thought is why you would send a Valentine to your children or grandchildren? I dearly love my 3 children and 7 grandchildren and try to express that in many ways but would never send them a Valentine card.
However, on balance, I guess that it doesn't matter how you show someone that you love them as long as you do it. That is the most important thing and we all do it in our own way. So I started this post with a sniff and ended with with a sniffle. A Valentine bouquet to all Grans. What a lovely bunch. ? ??? ? ?