My husband doesn't think we should replace my moms lawnmower or cell phone: Advice?re

So my mom watches one of my daughters full time. This is her sole income and we pay her well below market value for child care. She’s always flexible for us with hours and sometimes takes out other daughter if she’s in break. It’s amazing because we trust her and the girls have learned so much from her. At first we were paying her per day but recently I just found it easier to pay a flat rate (this is regardless of if my daughter comes, similar to how daycares go). We don’t have a lawnmower and we asked my mom to use it. While my husband was mowing it stopped working. He asserts he did nothing wrong and it’s just a piece of junk. I offered my mom to fix or replace because it was broken while in our possession. A week later my daughter threw my moms phone in water and broke it. I ordered the same solution to her. My husband is upset because he feels we pay her too much and that should offset for the lawnmower and phone. I disagree as they are two separate things. I want to know what y’all think because it’s really eating me up/making me mad how he’s reacting. Thanks!