I'm using an app and it explains the comparitive to Klein is Kleiner. Then when I go to the practice page (it's a full in the blank) it says "Peter is the smaller child. Peter ist das (blank) Kind." I write "Peter ist das kleiner Kind." It said I was wrong the answer is "Peter ist das kleinere Kind" Where did that extra e at the end come from? Why is it added?
Pudge, alas, adjectives take endings according to gender, case and...
...presence of articles and some other determining words with similar properties:-/ They try to expain the underlying logic in the article above.
The "e" comes from the (weak) flexion of the adjective according to the (singular) number , (neuter) gender and (nominative) case of the noun "Kind".
Peter ist das "kleinere" Kind. but that does not even sound very well. we would say "Peter ist das jüngere Kind" (younger)
The folks above are correct. In German, even the adjectives follow a declension pattern.