I would book a cancelable(non-priceline)room at the sheraton downtown LA/you do not need a car-the subway stop is right across the street And this property is close to the CC or a cheap cab rideThis will save you $25 a day in parking..Take the flyaway from LAX.
The day you decide to go to Disneyland you could rent a car.There also is a Disneyland express bus from LAX.

Since you plan to go to disney before hand You might want to consider the following/Arrive LAX rent a car at the airport location if your agreement will let you return the car at a downtown LA location-fantastic!If not,on your way back from OC take the 405 instead of the 5 freeway(this is a 20 minute detour)since there are two of you you will be able to use the diamond lane(part of the way at least)and drop the car back to the LAX rental location.Take the flyaway from LAX to the downtown sheraton-which is offering triple points right now BTW.No need for a car to attend the convention-just a hassle as you would have to pay for parking at the hotel and again at the CC.BTW there is a subway stop a block from the CC-have used it many times.

A 10 year old might just love downtown LA,the architecture is very good and it would be a great experience for a kid to see what city life is like.