As a single adult I'd say more cost effective booking a hotel room. Crieff Hydro used to give me a single person discount. Fab place to be on your own with children because there is free childcare so you can have some alone time, and enough to do with kids when you want to.
Coylumbridge is a good shout. Loads to do and very child friendly. Landmark is probably the very best park I've been to (and we've done Disney, Alton Towers etc)
Might get a good deal in a Glasgow, Edinburgh, Dundee or Aberdeen hotel as there won't be the demand for rooms for businesses over Easter. Loads to do in each city:
Glasgow: Science Centre, Transport museum, Scotland St School
Edinburgh: Dynamic earth, Camera Obscura, Castle
Dundee: Verdant works, Discovery point, Unicorn
Aberdeen: beach, Satrosphere, Codonas, loads of parks
Have fun!