Children aren't adults
Children are not little adults they learn things primarily through experiences and modelling their parents, rather than through verbal explanations. Being kind to your child is more effective in teaching kindness than an explanation of why it is good to be kind (although the explanation is also important).
Children are not able to control their emotions the way that adults can. Their emotions are overpowering and they are still busy learning how to control them.
In order to realise their potential children need to feel safe. They need to know that their parents can look after themselves. For instance, when a parent is constantly overwhelmed by their own emotion, children feel like they need to take on the parental role. This is deeply anxiety provoking for two main reasons. Children need to feel like they can depend on adults in order to feel safe. Also they are not developmentally ready to shoulder adult responsibilities and so are bound to fail and feel like failures. All of us parents go through bad patches. If you are going through an extended period of depression etc … the best thing to do is seek support from other adults - family, friends or professionals.
What parents say has an impact on children. Even if our children don't respond to what we say, they have heard us.
Children are more sensitive to non-verbal messages than to verbal ones. They can read our moods, non-verbal responses and internal judgements. Put another way our feelings and actions are more important than our words in our relationships with our children.
Parents don’t have to be perfect, just good enough.