This is a post I have been thinking about writing for some time after reading a comment that preschoolers are not capable of metacognition... and yet I have seen young children thinking about thinking... and using it to their advantage. I would say that metacognition features strongly in young children's learning... it may not always be verbalised the way adults are used to being able to recognise it as metacognition.
For instance children, from the very start, observe and learn. They watch others, test things and adapt what they see to their own context. This is easy to see when young children are trying out knew motor skills... they observe others doing something and then make the decision to try that out for themselves - they have to think about the movement, they have to consider whether they want to also try it... and then afterwards they assess whether they were successful or whether they need to do it a different way to be successful. Children are clearly thinking about their thinking and not just their actions and the experience.
The advice is not always going to work (sometimes there are physical differences, for instance a taller child is going to be able to reach a better foothold that a shorter child cannot) - but they then think through this together and try to devise a new way for success.
I often film the children in their attempts... so they can look at what they are doing and learn from the footage. What they thought was a good idea does not look as successful on film, and sometimes what feels hopeless in real life suddenly looks more hopeful on film.
Getting the children to pause and reflect on their activity - not only opens up the opportunity to think about their physical thinking, but also creates a space to calm down and allow frustrations to die down so that only determination is left. Frustration can be a good thing - as long as it does not get overwhelming.