Jealousy begins at a very early age; we are wrong to believe it surfaces first in the dating stage. Speaking from years of working experience in childcare, I can testify that infants and toddlers become very jealous.
There is the common jealousy over toys, but another is even stronger. They are extremely possessive of those they love, and do not want to share them with anyone. If a parent or caregiver is showing more attention to another child or a child becomes too involved, jealousy is the natural reaction.
Two examples come to mind; the first makes me smile. I worked with two year olds and heard a disagreement between little boys that went like this… “My Miss Pam!” The boy received strong disagreement. “My Miss Pam!” It seems both wanted me all to themselves. The second brings back less pleasant memories. One infant held my attention; the jealous girl standing below me took a bite out of my leg!
“Beware lest you break the contract the Lord your God has made with you! You will break it if you make any idols, for the Lord your God has utterly forbidden this. He is a devouring fire, a jealous God (Deuteronomy 4:23-24 The Book/ Living Bible).” Our sovereign God refuses to share us.