My DD (5y 10m) has always been an introvert. I have posted about this on here previously.
But I didn't realise quite how bad it was until she's started coming home with injuries from school (scraped knees with blood soaked tights, an bump on the head from falling over etc) I asked her why I didn't get a note about the huge bruise she had on her head and she said she isn't telling anyone about these accidents if they happen when she's alone!
I have always told her no matter how much you don't feel like talking to somebody you must always tell a teacher if you get hurt, feel poorly, need the toilet or someone has hurt you.
It absolutely breaks my heart to think that she'd rather walk around in pain all day than face telling someone she's fallen over. I have no idea how to approach this or what to say to her.