Building on @Mandy123's suggestion of online resources, I am wondering if you have come across the Raising Children's Network before? They have some brilliant resources for children of all ages.
We often refer to their resources and I have just had a search to see if there are any that might be relevant for you. It depends on what action you are thinking of taking if you are concerned about a parent-child interaction. If you want to talk to the parent about some resources that might help them, then I would recommend this article about good parent-child relationships and why they are important, and this section about toddler behaviour. It also links to other articles that the parents might find helpful too!
You have mentioned emotional abuse, and there are some resources out there that cover this topic too (not necessarily a on stop shop, but a collection of resources). ReachOut have this collection of articles about different types of abuse. It is for a youth audience, but still helpful. We would also encourage you to read resources by your local child protection service (for NSW, Australia that is Family and Community Services) which gives very good definitions of what emotional abuse looks like, the signs of emotional abuse a toddler may express, and some steps on what to do. Here are some descriptions of domestic violence including emotional abuse in NSW. Definitions of emotional abuse are very specific in different jurisdictions, so it is worth noting what the definition is where you are and whether the behaviours you have noticed fall under this category.
I noticed you mentioned you were in this child's circle, do you have a good relationship with the parents?
I hope this helps to give you a few starting places Let me know if you want some more ideas and I will see what I can find!
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