Try to be #understanding as they may not know how to tell you how they are feeling but are making it apparent though their behaviour. So try to look beyond the behaviour and stay calm.
Make then feel valued and show them you #understand how they are feeling and support them. This can start at a young age they will soon learn that they can be upset but they will have someone to listen to them when they are ready. For example, “It sounds as if you are not ready to talk at the moment. I #understand that completely, but I am here whenever you need me.”
Try not to criticize
When your children are having a mood swing, you will feel the urge to point out that they are overreacting and that the world is not going to end but try to remember how you would feel if your partner for example said this to you when your feeling angry or upset ekkkkkkk that would go down like a tonne of bricks here dunno about your house, you want to ensure their thoughts and feeling are validated and important to you (even if the seen silly to you it means something to them so try to be respectful of their worries) .
Spend time with your child
When they are feeling distressed or moody perhaps we will call it why not take some time together, go for a bike ride, kick a ball around in the backyard, play a game something that may interest you both gives them the sense that they are important once they feel comfortable and a little more relaxed (if at an age to do so).
If they are younger they will appreciate the time nonetheless and perhaps redirect them to a more relaxed state as they focus on something else and get some extra attention that they may just need.
Create a happy place.
Perhaps a calming place can be created when it is apparent that they are having a struggle with their emotions. This can be a simple bean bag in the reading corner, maybe a space with calming music and quiet activities it depends on your child, explain that we all have days where we feel overwhelmed even as adults and that’s okay its how we deal with them that’s important.
Eg when mummy feels upset she makes a cup of tea and likes to have some quiet time reading to calm down what do you think would help you? My actual life saver is going outdoor if im feeling in a mood… something about fresh air (and not doing housework just forgetting it for awhile really cheer me up) do something that helps YOU calm down try and find your happy place too so you can share this with your child showing you are on the same page and its normal to need some time out from life.
Or if they are younger maybe you could help them create such a space that they can go to when they are feeling overwhelmed with life. If we teach our children how to cope with their emotions now, it may have such an impact on their whole lives and relationships.