Beth and Gary's place was perfect for our family of two adults and two kids (5 and 7 years old).
Checking in was incredibly easy, and Gary was there to greet us (but key was in a lockbox, too). The place was spotless and all the goodies in the fridge and pantry were greatly appreciated. The kids gorged themselves on the variety packs of cereal!
The beach was right out the back gate. We enjoyed our morning walks on the beach, and then headed into the city to explore (about 15-20 minute drive), coming home again in the afternoons to hang out at the beach again or at the playgrounds (about three really good ones in the near vicinity). The kids especially enjoyed the body boards that were available and we felt safe swimming between the flags a five minute stroll down the beach to the surf lifeguard club.
Cannot recommend Beth and Gary's place enough if you're looking to get the best of both the city and beach in Christchurch.