I don't think it's all that weird for GPs to provide toys for the dgc to play with at the GPs' house.
My parents have always had a stack of toys and books ready for my dc. They had placemats and dishes specially for the dc. My parents bought a cot, and I used to leave a supply of bibs, nappies, wipes, etc over there. When we lived near them there was a whole corner of one room which was dedicated to the entertainment of my dc.
My ILs, OTOH, never did anything whatsoever to accommodate the dc. Not even moving FIL's classic car/aeroplane/train models to a higher shelf where they wouldn't torment toddler dcs. We always had to bring everything with us, including toys and books, and constantly monitor the dc so that they wouldn't touch precious things. That, to me, was extremely weird. Made me feel soemwhat unwelcome.
It is only in the last year or so, since our eldest turned about 8, that they have provided anything in the way of children's entertainment. And last Xmas, for the first time, they showed our dc a shelf where they could help themselves to some board games, puzzles, colouring pencils and drawing paper.