Blackpool is great at what it does; low budget entertainment. If you go expecting fine dining and Florida style attractions you will be bitterly disappointed. It's a tired looking place but has advantages over other seaside towns in that there is more to do.
I have stayed in the big blue hotel, it's very good. Rooms are nice and clean and as previously mentioned its right by pleasure beach.
For a child of 3. There is sea life centre, tower and some parts of the pleasure beach. For the grown ups there are some decent rides in the pleasure beach too.
Food, lots of chip shops and take away joints. Plenty of family pubs too.
Blackpool is what it is and if you go there knowing that then you will be ok. That said, I wouldn't thank you for a trip there. I went 5 years ago after rose tinted memories drew me back and was saddened by how tatty it has become. Now I only go if there is a gig on or the wife and I fancy a ride out to one of the epic fish n chip shops....