What is 'adopt as care dependent'?

"MissDirect;c-16336298" wrote:
Does anyone else have an issue where a non-related caregiver (definitely has the child/teen as a care dependent, I checked) won't get certain milestones for parenting achievements unlocked? specifically these goals:

Super Parent: Have a child with a character value within range to receive a trait
Successful Lineage: Have a child earn an "A" in High School (not sure if the "have a child max any skill" one is affected too, haven't gotten that far)
Big Happy Family: Be a parent to a child with 3 friends
and Be friends with 3 of your children (only two kids in household but the counter by this still says 0/3)

All of these unlocked just fine for the kids' biological parents.

I have highlighted the important spots in your post.
The reason of this is simple: Caregiver is not the child's parent. They are one of two groups of sims who will check on the child and raise them.
Like I said in the previous post, caregivers can be either related or unrelated sims (that aren't their parent) in the same household as child who will take care of them with parents. I quote my previous post here. I hope it helps.

"EgonVM;c-16073798" wrote:
Ok. Time to explain.
Young adult, adult and elder sims can adopt toddler/child/teen in the same household as care dependent and kids can make adults in the same household as their caregiver. Caregivers act like parents, but there is some additional information that you need to know.
Adopting a toddler as care dependent doesn't require any game packs and can be done by teens. While all sims can fulfill toddler's needs, parents and caregivers will make sure toddler stays happy. If Parenthood is installed, caregivers can also do Parenting actions to them.
Adopting a child or teen as care dependent will require Parenthood game pack and cannot be done by teens. Caregivers gain access to Parenting interactions, meaning only parents and caregivers can punish and encourage them, help with needs, influence/force them to do something ect.
Note. Teens cannot gain Parenting skill.

Another note. Sims outside of kid's household cannot adopt them as care dependent and vice versa.

Yet another note. If you have sim be a child's caregiver and then move them out, they'll eventually come back and stay at the house the child is living in. If you don't want this bug happen to you, remove them as care dependent/caregiver before moving them out.