You can't compare the whole of Cornwall or Dorset to Blackpool Ffs! 
That's like comparing a fry up at a greasy spoon with a meal at Claridges!
Blackpool is what it is. I have been as a singleton on a hen night, hated it. But as a parent with young kids, it's great.
I tend to hang around the seafront and piers. Not interested in the shops and it is therefore away from the bar's and drunks.
It does have problems, just back from the tourist front, but there are also some beautiful houses around the area (on the way to the zoo and up the coast and on the way to Fleetwood, in the quieter parts of town)
Really bizarre for some on the thread to comprehend....you can enjoy Cornwall and Blackpool, I do.
I personally despise New Quay I went about 10 years ago and swore I'd never go back, dirty, drunk teens, over priced, packed. I've stuck to Looe and the quieter seaside towns, much nicer.
Brighton - have never got the hype. Dirty and so far up it's own arse I'm surprised the locals get enough oxygen to survive.
Yet people rave about the places.
Personally, a weekend stay with children in Blackpool isn't something I'd do. But as plenty of others have said, stay nearby and do a day trip, very enjoyable and its in a beautiful part of the world.