For a family with kids..antalya or fathiya will be a nice holiday??
Mainly because of the larger hotels with additional family-orientated activities.
I found Fethiye to be a working town without much in the way of tourist activities. Obviously there is Olu Deniz beach not far away (the local Calis beach I found to be too pebbly) and further afield, Sarigerme had the best sandy beach in the area, but nonetheless I found Antalya superior as it caters for tourists.
Not sure how convenient it would be for you to fly into Dalaman airport, but Antalya Airport is very large and busy, with direct flights to numerous countries.