How do you decide whether to make something a gift to both (all) your kids, give it to just one kid, or buy two (or more) of the same thing to give one to each kid??

I have two boys who are only 21 months apart and they are interested in all the same things. I'm really struggling on how to figure out what to give each kid without having to buy two of everything or having them be disappointed that they didn't get something the other did OR forcing to share EVERYTHING.

What do you guys do?