This has a sound that is easy to recognise but often hard to say! If your child has trouble with this sound, encourage them to take their time and s-t-r-e-t-c-h or 'chunk' the word. It can be tricky when it is in the middle!
'Sh'is a digraph using 's'. Digraphs happen when the letters make a different sound together, than they do on their own. Say the sounds separately then join them together snd you'll see what I mean!
Talk about s sounds and the sh digraph with your child- make a list of words together. See if they recognise s blends like st, sm and sl too.