Buy a better bike if you want the kids to enjoy cycling. It'll stay ridable and reliable longer, you can recycle from one kid to the next as noted, and it will have a little resale value when the second kid grows out. Buy a little large to start with to maximize your time with the bike. I'd try to get about 3 seasons per kid on a bike.
I got burned with an XMart bike when it was a couple months old and the freewheel gave up the ghost just before a ride. My daughter was very disappointed, almost to a point of tears, to not be able to ride. is that worht the $50 you'll save to you?
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Tom
"It hurts so good..."