Possession

We only recently got out the old box of Lego that's been hors de combat for nigh on 20 years. (Lego is the more advanced version of Duplo bricks - both can be used for building designated or free-form constructions).

Six-year old was immediately very keen, and so of course was her sister (who will never admit to anything being too challenging.)

Recently, the former asked us to bring the Lego box over to their house and we could have the marble run in lieu.
( I got a sneaking suspicion that the marble run has fallen out of favour...)

Perhaps not,  I said, the Lego box lives here and will be here for you to play with.

(As grandchilden get older, and grandparents... get older, some form of incentivisation may be required to bring the two together.)

Possession is nine tenths of the law: notice the expression on the little one's face.