What kind of things would they like to do??

As for going out, London can be one of the hardest places to find a good night out in!

You really do need to do some research into what exactly you are looking for.

The obvious ie Leicester sq, Covent garden area are such tourist hot spots that they do invite the intimidating factor. You need to be wary of some who will try to take advantage of some young naive wannabe party types.

Hi Millie

i know what you mean about naive young adults, my daughter has her head screwed on but a couple of her friends are a bit dizzy and would probably believe anything they were told.
They will be looking for nice, cheap resturants (are there any in London? probably not!!) and maybe some nice winebars

Bisto 1 is a chain of 4 mediterranean restaurants in Covent Garden & Soho, they do 2 & 3 course meals for £9.90 & £10.90 & they're always busy. Look them up online

we went to a nice angus steak house in leicester sq near mcdonalds once, not sure if its still there..

Bistro 1 suggested by mickyjo is good value also Cafe In the Crypt if they want something unusual and don't mind canten style. One reasonably priced but very 'different' restaurant I love is Sarastro on Drury Lane, great if you can go on a Sunday and catch the live opera!
http://www.bistro1.co.uk/
http://www2.stmartin-in-the-fields.org/page/cafe2010/cafe.html
http://sarastro-restaurant.com/

Bar prices in central london can vary wildly but Lab Bar is good for cocktails, also Dirty Martini when they have happy hours. Really depends on what they're looking for bar wise, you have trendy (if a little pricey places) such as the Long Bar and Jewel aswell as the regular chains such as All Bar One and Tiger Tiger.
http://www.labbaruk.com/
http://www.dirtymartini.uk.com/london/cocktailbar/index.asp
http://www.sandersonlondon.com/en-us/#/explore/?id=/sanderson-london-long-bar/
http://www.jewelbar.com/

we went to a nice angus steak house in leicester sq near mcdonalds once, not sure if its still there..

That was still there just before Xmas.

There's a pub just down the little side street by the Prince of Wales Theatre called the Billy Budd. An excellent pub meal for about £6.99, but they do stop serving after 1900 or so. Good beer at a good price - for Londinium.