Well, my Art Director rightly pointed out that we can't very well use the same design for the endpapers at the beginning of the book, because a) it will spoil the joke and b) nobody will understand what it's all about yet.
So I set about thinking up other, more normal activities that Sparky and Lucy could share. It took a while, as I wanted them to be either cute or funny or both. I also needed situations that didn't require either backgrounds or large props: making sandcastles at the beach was out, as was playing on the swings. I did adapt both the beach idea and the park though: