Me and dh (without the dc) stayed in Margate for 2 nights last year as a rockabilly band I like were playing one of the pubs.
We stayed in the Sands hotel and it was very nice.
We did go to the turner but I'm not a massive art fan anyway so we were in there maybe 20 minutes.
The beach is lovely and sandy but of course you need the weather for this.
The shell grotto is worth a look I liked it shellgrotto.co.uk/
Dreamland we went too as I wanted to go on the scenic railway and the wheel. We enjoyed it
The old town I really liked but then I love the retro/vintage shops so it's right up my street.
We had dinner at the Ambrette theambrette.co.uk/margate.php?utm_source=local&utm_medium=organic&utm_campaign=gmb I couldn't believe how good the food was but that might not be the right restaurant with dc
However the GB pizza company would be a good one for with dc, we ate here the second night and the pizza is good. greatbritishpizza.com/
The bernies choclate bar was nice. Lovely waffles and hot chocolate
Yes some of Margate is run down but there is a lot of beauty too.
As others have said you can use Margate as a great base for visiting other places;
Dover castle
Canterbury
Deal & Deal castle
Whitstable
Broadstairs
There is an RAF museum near manston
Quex park
Wigham wildlife park