help with occupying GS and GS long distance during lockdown!

I also do the kims game thing. They would probably like a quiz. I did one about me basically. What is granny’s favourite colour. What colour is granny’s car. What does granny like doing etc etc.
I bet there are story books in French and English available,

What about drawing? Perhaps a “guess what it is” and you all take turns - maybe just draw a body to start, then a head and so on.

I sometime play a memory game with my far away DGs aged 4 and 6. Put 5 objects on a little tray e.g. lego man, felt pen, spoon, sweetie, photo...can be anything . Have them look carefully. They then close their eyes and you take one object away and move the objects around a bit ( or not, depending on age/ ability) They open their eyes,and guess correctly the missing object . You could use both French and English for the objects .Children love this kind of game. They can prepare a tray for you to guess at their end . You are lucky to have an hour regularly . We have a facetime about once a month at our request as we miss seeing them as they have just newly moved abroad . Ah well .

On practicalities, we’ve found Zoom is much better than Skype.

My 2yo GD was entranced yesterday when I took her on a ‘tour’ of my house on my iPad. She loved seeing the things she’s familiar with on her pre-lockdown visits. As your GC are a bit older you could combine that with the English/French words idea.

It is hard, though, small children have short concentration spans.

Maybe it's a good opportunity for them to practise their English. You could give the name of something in English and they have to go and find it. They could also tell you its name in both French and English when they've found it. It's an active thing for them to do and just doing a few words each day should stop them getting bored too soon.

Not easy. I used toys/puppets to play Boo and for make up stories. But can’t see wee ones sitting for a full hour.