Me and my partner did a week's motorbike touring round south-west Ireland last year. We didn't have kids with us so can't advise you specifically about that. However, it IS expensive! We thought more expensive than here – averaged 150-200 euros a day for accomm and food, although we didn't book anywhere in advance so some nights we got bargains and some nights we ended up paying quite a lot.
We loved Kinsale which was very pretty, if a bit touristy, and also Kenmare which is just below the Ring of Kerry. We did the Ring of Kerry but were more impressed with the Beara Peninsula which is just below it (more unspoilt, more spectacular scenery and less people!). Hospitality and food is generally excellent where-ever you go. We also enjoyed Dingle (the town on the Dingle peninsula – which is a spectacular drive if you care to do it) which isn't the most picturesque town but has some good pubs and plenty of eateries. Dingle is also where they have the 'tame' dolphin in the harbour and they do boat trips to see it which the kids might like. When my girlfriend when on it she saw other dolphins too. They guarantee that you will see a dolphin or your money back usually. The highlight for us were the fabulous coast rides on the bike, the pubs, hospitality and food!
Waterford is a nice town, bigger than some of the others mentioned above, so plenty of choice of places to stay. We never went to Cork so can't give you any feedback on that. AVOID Killarney which is also on the edge of the Ring of Kerry but is very touristy and a bit tacky (all shamrocks and leprechauns….).
As far as accommodation, we tried everything really – hotels, B&Bs, pubs with rooms – and only had one iffy one. The rest were all good and any shortcomings were usually made up for by the atmosphere and helpfulness of staff.