I can't help but worry that some children are being underestimated 
They can understand the concept of delayed gratification by 4 yrs, i.e ''we will get an ice cream after we have done the shopping and put it away, ( I'm not saying they're always happy about it) because it's often practiced frequently, especially if you have more than one child.
And yet, some think that the same 4yr old can't understand non-instant/ delayed punishment
i.e ''I told you that if you hit your brother again you would not be allowed to watch TV tonight'' Yes, they may well need reminding, and they won't be happy about it, but that doesn't mean they don't/can't understand it 
They can understand cause and consequence long before age 4, they are usually masters of it by 2 yrs. i.e. They do a particular thing or behaviour to illicit an expected result i.e When I press this button, my car comes out, or when I keep getting out of my bed at night, Mummy comes and sleeps with me etc
Many children have been attending nursery (some even at school at age 4), and they have been 'remembering' everything..................friends names, what toy goes where, nursery rhymes, what happens when it's snack time etc Everything learned by experiencing, repeating and practicing. That's also how they learn about consequences for bed behaviour, experiencing, repeating and practicing.
It's up to the individual parent how they choose to discipline their child, and everyone has their own way of parenting, but be careful not to underestimate the level of development of your child has reached, and what they are capable of.