CC is not the same as locking your child in a bathroom or any other room. CC done properly is never leaving your child to just cry them selves to sleep, you go back in all the time at very short intervals and reassure your child that you are there but it's time for sleep now.
A child learns its behaviour and if they learn that sleep time means either being cuddled to sleep or up and down for drinks or when they cry they will be picked up that's what will happen night after night, why would they suddenly decide to change as they don't know any different routine?
Teaching a child that it's night time and it's time for sleep is a good thing - my next door neighbour has a 2.6yr old ds like me and her ds is running around at 11pm in adn out of different beds because she doesn't want to teach him what bedtime means.
She thinks she's doing theright thing and cannot bear to hear him cry (even though I've told her and told her that CC is never leaving him to cry himself to sleep), but then her ds is so tired and grumpy adn moany during the day that he drives her mad - she can't cope with him and she shouts at him and he is unhappy.
I don't agree with what she does but I can't make her change.
Locking a toddler away in any room (why on earth the bathroom? my ds would have flooded the place or drowned himself if I'd have done that) is horrible imo, though believe me I have felt like it when ds is wrecking everything and screaming when I'm trying to do something with the older 2, but that's what toddlers do. My dd's did the same so I knew what to expect with this one.
Change the routine if you want quiet time with the older kids. Toddler can be in bed asllep at 7pm and then you can read to the older ones.