I started my daughter with a PSE mini burner. She did well with it until she was 13YO. It was a bit smaller and lighter then the atomic if I remember correctly.
I bought my 6Yo a compound bow for children off Amazon for $100,(pandaras) it shoot great for what it is. He is a lefty and cannot use his sisters bow.
Their is a fine balance with draw length, draw weight and bow weight for the very young kids.
Arrows will be important, you need light arrows, most that come in a package deal will be too heavy.
may best advice is use some type of reactive target. They quickly get bored of shooting at a colored circle. Small water balloons, clay pigeons or ping pong balls would keep mine shooting all day.