We do topsail 2 - 3 weeks a summer and with 3 kids (4th on the way) all 7 and below we've done many a trips with 1 year olds. Topsail is a fantastic beach for this as it's rarely overly crowded and just a great family beach.
Topsail Realty is a good rental company. Treasure Realty pretty much has the monopoly on the newer, larger beach front homes on N Topsail and and we use them simply because we have to. They are expensive, rude, disorganized, unprofessional and have absolutely no appreciation for their customers, but again represent the best houses down there so we just try to take them with a grin.
September is a great time to go. If you are beach front and not next to a public access lot it's like having your own private beach. It's also considered mid season not prime so you can find some great savings on homes.