There was much more to Adam and Eve's time in Eden than idle playtime.
Gen 2:
15) And the LORD God took the man, and put him into the garden of Eden to dress it and to keep it.
Also:
Gen 1:
28) And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth.
God told them to be fruitful and multiply. They sinned before they even conceived their first child.
It is reasonable to conclude they were not in the garden very long.