Boy stuck for summer with grandparents

Looking for this book since I read it at in late 00s, a boy spends the summer with his grandparents (or possibly other relatives) instead of Disney because he stepped on a rusty nail and had to get tetanus shots etc. His family goes without him and calls occasionally, but he is stuck with relatives. He goes out to the beach a lot and meets locals, specifically a woman rumored to be a witch and gets to know her. It's not a magic book and I don't think she was a real witch. The kid's name was gender neutral, Ashley I think, and the cover of the book had red script lettering. I remember specifically a scene where he argued with his siblings about lockjaw because my hand was impaled on a rusty nail later that year and I had to get tetanus shots, and every time I think about it I wonder about the book. I posted about it on Reddit a few years back and no luck.