They definitely have a sense of who they want to be with and who they feel most affectionate toward and who they want to turn to when they need assistance. Not only are there advances in behavior, but I do want to point out that the toddler period has two very distinctive qualities in addition to those that I mentioned. And that is, there is an increase in irritability. Yet there has to be some restraints placed on toddlers. And the second behavioral change is a dramatic increase in autonomy.
Some children get irritable if their noses are wiped.
Some get irritable if they're told they have to go outside. Just swoop up the toddler, grin and bear it. And the reason is that at 18 months of age, toddlers don't have a lot of language. That brings a certain amount of frustration. Just bear in mind that this is a period that will end.