Its not a bad gesture but my thought/fear about receiving something like that is I'd feel the need to reciprocate. I'm not saying you're doing it with that intent but it could create some unintended awkwardness. My vote is "no" but its not a horrible thing, if that makes sense.

In my family, some of the women bring gifts (usually a plant or flowers) for each of the moms. I don't think it's strange at all, it's acknowledging motherhood in general.

The only problem is now that I'm about to celebrate my 3rd mothers day as a mom myself, I'm thinking "crap, do I have to buy 4 gifts now too? What's the etiquette here?"

But that's just me. I don't hold it against them, it's just me being a little socially awkward. If you have a generally drama-free and well-adjusted family, I doubt there will be any animosity, nor will they expect gifts next year. Maybe you could explain the gifts by saying you've been on an earring-making binge lately, which could make it seem like you have too many earrings and you thought they'd like them and this is as good an occasion as any to give them away.