Honeymoon Bay/ Renfrew
Along The road from Honeymoon Bay to Renfrew has some hidden stops. One of them has one of the largest old growth trees only 10 - 20 m off the road if I remember correctly. Avatar grove is somewhere close as well, I think it is up the Gordon River road when you get down to Renfrew. Search online for some stops along this road.
The beach in Renfrew would be fun and is similar to Long Beach in Tofino.
If you have a small boat or canoe the estuaries of the two rivers, San Juan and Gordon on either end of the beach would be fun to explore. Good fishing as well.
Cowichan River is a world class fly fishing river but for the kids the most fun would be renting the inner tubes and floating down the Cowichan. The upper part near city of Lake Cowichan is pretty relaxing. The middle part has some parts you may have to walk around depending on water levels. Look up the Tube Shack Cowichan River to rent tubes and I think they have a bus to drive you back to top.