Name the essential amino acid in children that is a non-essential amino acid in adults?

essential amino acids are those that we cannot produce while non-essential amino acids are those that we can produce by ourselves by nitrogen containing compounds in our body.

all amino acids are essential in the human body, as without them many reactions would be unable to occur

Tryptophan is one of the essential amino acids.

About half way down this page you will get a list of them and the roles they play in our systems: http://www.realtime.net/anr/aminoacd.html

an amino acid that the body can produce without supplementation and includes glycine, alanine, and serine