Try Premier Inn at County Hall, great location, or further along the river at their Southbank one, great large family bedrooms. It gets booked quickly though. It's near to all the restaurants, giraffe, wagamama etc, and perfect for London Eye, Aquarium and Duck Tours.
You can get a boat from just under the Eye, that takes you to the Tower of London, that's a great thing to do.
Buses also go from there too, over the bridge and into the centre.
If you're driving I'd prob stay in the suburbs as parking can be atrocious further in (unless you find a hotel/B&B with parking included).
How old are DC? The Natural History, Science and V&A Museums are all next door to each other and are free. Duck tours are fun, but not recommended for under 3yrs. London Eye (pre-book to avoid queues) is next door to the London Aquarium.
Lots of places offer 2for1 deals if you have a travel card - you may need to google that for the T&Cs.
We'd like to take the DC to see the sights/attractions of London over the Easter weekend, but haven't a clue where to start I think we should take the train as it's a long drive (Devon), but I know dh would prefer to drive........so I guess we'll be driving. Would it be best to stay in the suburbs and train/tube in each day or stay in "the city". Any recommendations would be great, as to location or even specific accommodations. We'd rather have somewhere quiet-ish and not too pricey! Thanks in advance :-)