I'll throw it out there and suggest Exmouth is your better option. Both places have grewt ramps, but from a family view point there is much more to do in Exmouth. Coral Bay seems to be a 1 trick pony with a nice snorkel beach but limited options on where to stay and no shopping or sight seeing..

Exmouth has both sides of land mass to fish so you can be safer, shopping, an actual town, plenty of places to go look at like mangrove Bay etc and heaps of accommodation option to suit most budgets

 Exmouth for sure with a boat that size

as feral said probably a bit more to do 

we were in coral bay last year with 6 and 10 year old. They loved it.

skim boards, diving, whalehsark, fishing, being able to walk to the shops themselves. I’d go coral bay. 

 both places have pros and cons. it all comes down to what you like doing. 

as mentioned there is more ramps to chose from in exxy but require more driving . options are better when it comes to wind direction as well. also there are more beach fishing optiond along with more touristy things to do with the kids. 

Coral bay is more the place to go and relax . there is only a few shops in town to chose from but all within walking distance. the boat ramp isnt too far from town . if the kids like their swimming or messing around on the beach it is great with plenty of clean rock free beach to walk along. 

as far as boat fishing , you dont need a big boat to access good fish in either place. in coral bay there is a south passage and north passage well marked out. but if the wind and swell is up it can be tricky to get out the south passage . you can fish on the inside of the reef but make sure your outside the sanctuary zone. 

we prefer coral bay but we dont have young kids to think about.