Hi, there's a farm park in llandudno, which is about 11 miles from abergele, web link here bodafonfarmpark.com/ and also an indoor softplay type centre, which might come in handy if it's raining... bonkerzfuncentre.co.uk/ - it's aimed at all ages, certainly adventurous enough for an 8 yo (my 3 and 5yo love it there, but it's a bit daring for their age group really!) also, there's a tram that goes up the great orme in llandudno (every 20 mins or so, every day) - little cafe at the top and fab views for photos, well worth a visit if weather good. few other things of interest in llandudno too.
Bodnant Gardens www.bodnantgarden.co.uk/ is national trust, about 15 miles or so away.
Conwy is a nice little town to wander around, and the castle worth a visit if you go there. (again poss 15 miles or so from abergele)
And Betws-y-coed is really popular with visitors, bit further away, (20miles maybe), but plenty of little cafes and shops and lots of outdoorsy type things to do in the area, lots of walks (flat and within the forest areas) and swallow falls a couple of miles out of the village worth a look.
If you're happy to drive a bit further, then there's lots to do on Anglesey, www.foelfarm.co.uk/ and www.angleseyseazoo.co.uk/ are right next to each other, the beaches are better on Anglesey too.
www.portmeirion-village.com/ (further away)
www.welshmountainzoo.org/ (poss 6 miles or so from abergele)
These links will give you more ideas :
angleseyattractions.co.uk/
www.tentop.co.uk/
And of course if hiking is your thing, then Snowdonia and the mountain range are definitely worth a visit (and there's always the train up if you prefer the more leisurely option...)