I looked after mine at their house. I had a selection of toys/pens/books/activities/games/jigsaws (age appropriate) at home and each week I would take maybe two items along for something different to play with if needed.
We had a definite routine from Day 1 and rest times for Nanny and Grandad were built in. Breakfast together when we arrived, then getting dressed etc. Activity of some sort, then tea break/milk and snack, quiet time. Outing to garden/park/cafe for lunch ...or home for lunch always followed by 30 minutes of C beebies whilst adults had a bit of free time. After that, different sort of activity, cutting, sticking, colouring, water play, sand play, bubbles, music and children dancing (adults watching!) or maybe a game together age appropriate. Sometimes one adult took older and one adult took younger. "Helping" with getting their tea, change for bed, story and maybe a quiet game or more stories until parents returned.