I wish I could be helpful, but I don’t think I have enough information. If you don’t have younger siblings or have never babysat or been around small children, it’s no wonder that you aren’t comfortable around them. Working and playing with young children is a learned skill. You have to have kids to learn on.
Not everyone wants or needs to have children in their life. But in order to choose well, you need to explore the basis of your choice.
At 19, I wouldn’t expect you to have “maternal” instincts. Although there are many young women who are ga-ga over babies, it’s also true that some don’t have an ounce of maternal interest until they are much older or they see their own child. Remember, the word is “maternal” which means mother. Often mothering feelings come about when a person becomes a mother.
It’s also unusual for someone who is 19 to declare herself asexual. If I were seeing you, I’d ask you to explore your medical and psychological history with me to understand it. I’d also want to talk to you about your pessimism about ever finding someone who would love you and you would love in return.
I do think that looking into these issues is important to your own growth. I hope you will contact a therapist and go to therapy for at least a few months to learn more about yourself.
I wish you well.