Of course I chose that word because it's vague. I guess, if I have to narrow it down, it's a feeling that something is disrespectful.

I think people's reasons for having kids usually fall into one of the following categories:
1. It's what normal people do, so I'll just go with the flow.
2. I have an emotional desire for a parent-child relationship.
3. I want someone to take care of me when I'm old.
4. I want an extension of myself to provide me with a kind of proxy immortality.

It might be more obvious why I find 1, 3, and 4 to be disrespectful? So I'll just talk about 2, which I suspect includes the kind of "liking kids" that you are talking about.

Imagine that, from now on, as soon as a baby is born, it will be instantly granted certain benefits. The baby is given the size, strength, and agility of an adult. They get the intellectual capacity of an adult. They get an assortment of knowledge and skills implanted into their minds, well-suited to independent living in their society, and proof of having those skills. They get the wisdom, rationality, and emotional skills of an adult. But they do not get any episodic memories implanted. They don't come pre-loaded with any emotional attachments to specific people, which is just fine, because they have great emotional and self-care skills to support them as they meet various people and decide who they want to form relationships with.

Does this even count as a child anymore? Would a relationship with this person satisfy the parental desire in #2? I bet it wouldn't. All because the person is no longer weaker or more incompetent than the "parent", and is free to form emotional attachments of their choice based on getting to know people. Liking kids, specifically as kids, usually amounts to liking the weakness and vulnerability of kids. I have heard some people say that what they like about kids is their "innocence" but I don't believe in this innocence thing, except as a euphemism for ignorance. I cannot think of a single thing about my child psyche which was better than my adult psyche. My child self was more trusting, which I bet many adults liked, but I think my current state of being less trusting is better, and therefore the fact that those adults liked that about me was disrespectful--it was liking my weakness. Some adults may have enjoyed teaching me things. That is a case of them enjoying my ignorance.

I'm not so put off by people wanting to adopt kids, because they see a need that they feel well-suited to fill. But creating a brand-new kid because you want a relationship specifically with a small, weak, ignorant person who is almost guaranteed to love you? Icky.