I have 3 kids, ages 5, 3, 2. We travel in one suitcase as a family of 5 plus usually one backpack and my crossbody purse. At
Disneyland I did a Kavu bag instead of my crossbody. We can get away with the one suitcase for even 10-12 day trips.
We use packing cubes. Each child gets 1medium cube and then a small cube for smaller items. Each adult usually needs at least one large cube, sometimes a medium too. We don't put coats/sweatshirts and shoes in cubes and if our main suitcase is too full, then those go in the backpack (also helps with keeping things under the 50 lb limit).
I've found this method works pretty much anywhere (Disneyland, international trips, local trips, roadtrips, whatever) because then I don't even "unpack" the cubes but just place them in the drawer and unzip/tuck under the top. When we get to the end of the trip, I transfer anything unworn into one cube and place that cube back into the backpack, and the whole suitcase can be for laundry that needs to be done. If we're only going to be some place for one night at beginning/end of trip or if, for example, I'm concerned about luggage getting lost, I'll put pajamas and a backup outfit for each person into 1 medium sized cube and tuck that cube into the backpack that won't be checked.
When my kids were younger, I did the outfits in plastic ziploc bags method, including sock/hairbow/etc. That worked well for that phase of life too.