MrsMilton I gave some thought to your goals last night, and am avoiding work today:
To an extent it may depend on what the weather will be. In summer we alternate between fine weeks in the 80s to low 90s fahrenheit, and horrible weeks in the 90's up to 100+, with 100% humidity and thunderstorms, often in the late afternoon. Lots of thunderstorms.
If it is horrible, you may want to spend more time at Pentagon City which is a largely indoor mall (the associated Pentagon Row just next to it is outdoor).
Hopefully you will have many fine days. Georgetown is fun, but for priorities of shopping I would recommend Bethesda, Maryland and Friendship Heights as destinations ahead of Georgetown. Bethesda and Friendship Heights are right next to each other and both are on the metro's red line. Bethesda's shopping district particularly has many convenient, good restaurants right in with the shopping. There is also a very large Barnes & Noble bookstore there with a cafe, and -if you have small ones- the childrens section. B&N is a destination for parents of small children because of the good childrens section. Haven't been to that location in a year or so, but most B&Ns have a Thomas train play table.
There is a bus line that runs around the city to Georgetown and back, called the Circulator bus. Georgetown does not have a metro stop.
For denim probably the best destinations are (a) National Jean Co, (b) Denim Bar, and (c) Nordstrom (might be wrong about this but think Nordi's may be roughly comparable to John Lewis).
You can find the first two both in Bethesda and Pentagon City. Either Bethesda/Friendship Heights or Pentagon City/Pentagon Row have all the main shops of interest: J. Crew, Sephora, Anthropologie, National Jean, etcetera.
We also have lululemon shops here, the Vancouver yoga/dance brand. I think that their 'still pant' yoga trousers are, in addition to being very trendy workout gear, the ultimate mom gear. They can endure anything and look like new coming out of the washer, don't scream 'yoga,' and can be lived in throughout a pregnancy. Haven't done yoga since ds arrived 4 years ago, but live in lululemon. They also hem to suit, if you shop early enough - takes about a week to turn around.
The tricky bit about Target is that most locations are suburban and inconvenient to metro. You might get a taxi there, only to find it difficult to get a taxi back again. You might want to work with the hotel concierge on that question.
You might also want to look into a Whole Foods for their personal care products section. They have a lot of organic lines that might be exotic to you.
To target good dining destinations for your family, have a look at the chowhound.com message boards for Washington D.C. metro. People constantly ask where are good places to eat when visiting and get the most informed, up to the minute responses. Also see the dining guide at Washingtonian
Hope you have a great trip!