Just a random picture of this type of twins:
To be honest with you? I wouldn't have a clue! I'm sure my wife would but I sure don't. Sorry.
I depends on what their interests are. But if they are into electronics, maybe this kit:
https://www.amazon.com/SCL-175B-Snap-Circuits-Electronics-Discovery/dp/B00CIXVISU?tag=theplanetsorg-20
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