If your five year old likes hanging round zombies drug addicts, doesn't mind gangs of drunk Glaswegians, lives on reheated burgers and enjoys grey sea with sewage and horizontal rain, Blackpool would be a great choice.
Hated it - full of gangs of hen and stag parties all drunk and swaying along the prom from pub to pub. Very intimidating. I live not far from Gt Yarmouth and find that much more family friendly. Lots of kids attractions and arcades and a much nicer atmosphere.