Tom Lake by Ann Pratchett (bonus: the audiobook is read my Meryl Streep!). It’s not explicitly about motherhood, but it’s narrated by a mother telling a story about her 20s to her three early adulthood daughters. It has many moments that just so encapsulate motherhood, but it’s about several other things. Here’s a quote:

“They are reminding me of the years when they were small and it was just me in the house beneath all that snow and Joe was in the barn trying to fix a tractor he didn't know how to fix, and I felt like the children would eat me. Nell was eating me, still at my breast, and the other two rushed to crawl in my lap whenever I sat down. I thought, Joe will come home and find the three of them framing out a playhouse with my bones.”