NO!!! That is just plain mean. A .410 ain't a duck gun even with lead shot. Send me a pm and I will let you borrow an 20 gage 870 yute model and several boxes of shells.
I appreciate the offer but we are talking about 2 little girls and they may only be ready for the 410. If you let em get in close enough a 410 will work too.
I killed duck with a .410, but that was 30 years ago. IIRC, they do not make .410 SS. A friend of mine told me what he did, undo the crimp, take out the lead, and install steel. Reclose the crimp, and use some candle wax to seal back up. I never tried it, but he said that worked for his lil' girl.
A .410 will be fine for them to shoot. I would consider bringing a 12/20 to shoot some backup shots behind them for their confidence and to reduce cripples. Unfortunately, most of the steel I've seen is only available by the case.
You should consider buying some bismuth if you want to keep it non-toxic. (I've heard wardens say that they don't care about a child shooting a few lead shells, but I wouldn't push my luck either.)
I think Cabela's carries the bismuth in a .410, plus it'll have better knock down than the steel. It will also be a lot better for the barrel of most guns. Most .410's are full choke barrel only and you really shouldn't shoot steel from them. The steel doesn't compress like the softer heavier metals. The problem is that it'll run you $20/box.
Check back and let us know how the hunt goes. I'll be out in the marsh myself. Good luck to you and I'm glad others are taking the kids duck hunting too.