Decided to conserve my energy by staying close to main areas I am taking my grandson.
I know I can look on hotel maps but like to have personal recommendations.

The Marriott at Metro Center sits on top of a metro station and is two stops from the Smithsonian station. The stop before Smithsonian is Federal Triangle and it's the same walking distance from there to the Museums of American and Natural History, approx 5 minutes. Use the Smithsonian station for the Museum of African American History, Smithsonian Castle, and the Freer/Sackler Museums. Use the L'Enfant Plaza station for Air & Space and Museum of the American Indian.

Blue, orange, silver and red lines go through Metro Center so it's pretty convenient for other destinations as well.

I can't offer you any personal recommendations as I hven't stayed in any, but maybe clarify the question, as I don't quite understand the requirements. If you want to be close to sites (I'm translating that to near the Mall), why MUST it be the silver line? In DC proper, that is the same line as the orange or blue line, so I'm just wondering if there is some reason it must be silver.

If you want to be near the Smithsonian stop in particular (and many Smithsonians are not around there, but the other side of the Mall), there really aren't any hotels near it, that's federal land all around there. There is a HOliday Inn near the Air and Space Museum that is probably the closest on that side of the Mall (it's near an exit of the l'Enfant Plaza stop). There are just no restaurants on that side of the Mall, if that matters, for dinner.

Otherwise, hotels near Metro Center on the opposite site probably are the closest to the Mall. Hotels around McPherson Sq are on the silver line and not far, closest to the White House probably, but they are farther from the Mall than metro center if the goal is to walk, not sure.

A Marriott is pretty much a Marriott, never heard any complaints about it but if you only want personal recommendations, maybe someone will offer. I don't think that Marriott is actually connected to the metro station, even if it runs below it, although the metro entrance is only about a half block away. There is a Grand Hyatt near Metro Center, also, about a block away. The Grand Hyatt actually is connected to the metro station underground, although you do have that walk to it, about a short block. If you didn't want to go outside, that would be convenient.

That Marriott is really convinient - right above the Metro, easy to get pretty much anywhere.

Stay Alfred on 8th Street

https://www.booking.com/hotel/us/apartments-stay-alfred.html?aid=389181&label=metagha-link-mapresultsUS-hotel-1550875


(note $125 cleaning fee per stay)