i think maybe it would help if you could read the book yourself, it maybe talking about something entirely different from what you think it is. they have a new baby, could be that they want to learn how not to be toxic parents. i think maybe your thoughts on seeing the title of the book may have been what is bothering you.
i've read a book once on toxic relationships and my reason being was that i just want to know what was considered a toxic relationship, not that i thought i had one, i just didn't know what it was and i like learning and reading all i can get my hands on.
i'm sure that you have been a great mom. try not to awfulize the situation just yet, maybe you can talk to your son and asked him how he felt about the book, it may not be as bad as you think. sorry that the title of the book made you feel angry. i pray that you feel better soon.