If the sole focus of your trip is the Star Wars convention (and, if so, you have my sympathy ), then you might be happy staying somewhere downtown (Bonaventure often have very good rates for the weekend, check Priceline). But, downtown is not right at the convention center. The Bonaventure is a long walk away.

The convention center area is not especially nice or especailly safe--not real bad, just kinda blah in a big, rundown industrial area way.

IMHO, I would certainly rent a car, and would stay in West Hollywood, Beverly Hills, Westwood or Santa Monica. With a kid, probably Santa Monica is best choice. The entire area around downtown L.A. is no prize.

By the way, there is subway service to the convention center, depending on where you stay. And, you can take a Flyaway Bus from LAX to Union Station downtown for around $3 a person. But, Union Station is a couple of miles at least from the Convention Center and, again, not in the finest area. Not dangerous, just not very nice.