Thanks You Notes For Coaches How Do I Hit High Notes?

How do I hit high notes? - thanks you notes for coaches

I would like the high notes, as in "If I was a child," but every time I am on a high note, low to high as possible, it falls. and feels like instant messaging, singing through the nose and pharynx. How can this way to myself?
Not really a song, I have this little thing.
Thank you!