I help my mother with things around the house without her ever knowing it. For example, when I notice basic maintenance that needs to be done (like changing light bulbs or fixing broken things), I just do those things to lighten her work load.
I surprise my mom with little treats and small meals. I am not a great cook, but love makes everything taste a little better.
I do chores without being asked, such as loading the dishwasher and emptying the trash.
I also tell my mom that I love her daily, especially when I know she has had a rough day. I always thank her for everything because she sacrifices a lot for me.
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(By the way, this is what my kids would say they do for me to show how much they love me!)