Something that I talk about frequently when I speak to parents and carers is accepting children's feelings.
It simply goes like this... if you notice your child is feeling sad, recognise it. If you think they are starting to build up to some big emotions help them to understand it- " I can see you are getting frustrated/sad/annoyed". The more we help our children with the vocabulary for feelings, the more emotionally literate they will become- they will learn to read, speak and share theirs and other people's emotions.
This doesn't just go for those uncomfortable feelings, help them to recognise when they are feeling happy feelings too. "Wow I can really hear you are excited today!"
When we say validating emotions, it is about accepting how a child is feeling in the moment, even if you don't understand why or what they are feeling. "I can hear you, you are so sad". By doing this we are showing children that their feelings are valid and they will be less confused about those emotions.
Give it a try and let me know how it goes for you.