How to make first visit of grandchildren special.

They are staying 3 nights and we have kept in touch via Zoom fairly regularly. DIL not the easiest person,!

How long are they staying?
A welcome gift on their bed, as above, then later in the day , or on day 2, take them shopping to buy their chosen cereals / fruit / snack / sweets, and later another shopping trip for something appropriate to what you know about their interests.
But emphasis need not be on spending money. They will love being with you, in a home with different things to do, different rules, outings etc.
I miss having my grandchildren to stay as we moved nearer to them so there is no need.

Maybe a choice of board games, card games colouring books etc just left casually around for them to choose? Charity shops are good for this kind of thing and The Works is a good place too. Maybe ask them what they like to eat and shop and cook together?

Maybe a soft toy or other bedtime gift on their beds?
It will all be novel to them so no need to go overboard at the arrival stage.

That's a lovely idea but can i suggest you dial it back? how well do you know them? If, as I suspect, its not very well, then maybe be a bit lower key in your welcome and behaviour? Once you know them better and they know you then you can choose something appropriate, maybe choose together with them?

Maybe book a meal out on the first day ? A trip to a theme park ? Some new trainers ? (Or voucher for shoe shop/sports shop )
Make their bedrooms special ?

Take some photos of their stay and make it into a little photo book for them to keep. Maybe one each? You could send to them after their stay.