I don't have any resources regarding this, only a vague opinion.
I don't think going to kindergarten necessarily qualifies as "leaving a child". Some mental health conditions/symptoms (in adults, e.g. abandonment issues) can be linked to children feeling like they're being left by their parents, but to me that involves bad parenting (neglect, abuse and such). In the case of kindergarten, an example would be "threatening" your child that you'll leave them there and never come pick them up. If you show love to your child and care about their understanding of the situation, and if they're being treated well in kindergarten (which is another debate), I don't think it has to be a traumatizing experience. Pretty sure it also has some advantages.
Personally I believe I went to kindergarten at 3. I remember being terrified when my parents didn't come to pick me up for some unknown reason (pretty sure it happened more than once) and I was left alone until the late evening with one teacher waiting with me. That was not cool. But apart from that, I don't have really bad memories from kindergarten and I never felt like I was being left by my parents.
I don't think I've developed any abandonment issues nor social anxiety, but I don't know if any other ones can be linked to this.