Try Ingrid Flute for accomodation good selection of cottages /flats etc if you have a car try to get one with parking as it can be a problem in Whitby
My DS loves Whitby he has been going since he was 4 and now aged 9 still loves it.
Whitby Wizard science centre is fab even for younger kids it's near the crescent.
Bracing walk to the abbey always good .
Steam train to Goathland or up to Pickering if you have more time.
Sea life centre was good but pricey if I recall about £40 for three of us and we could only spend a couple of hours there...didn't really like Scarborough
Have been to Flamingo land the zoo part and the farm were good for younger children but the theme park bit wasn't my cup of (Yorkshire) tea - you used to be able to use Tesco vouchers to get in as again it was pricey
Fossil hunting at Runswick bay
The museum in the park at Whitby is also good fun and free DS liked it even when he was younger
Dalby forest great value for a picnic hire bikes or just drive through think it's around £8 per car and you could easily spend a few hours there
Hope the weather is good...my DS loves Whitby beach and we have a staycation week every year.
Great places to eat too Mounterays Italian very good and a couple of child friendly pubs near the abbey steps which do good food also The moon and sixpence- again good food and child friendly.
I love Artefacts shop too
Oh roll on August.