a growing child, a child in a period of rapid growth
育ち盛りじゃないわ
I'm not growing anymore.
— セントラル・ステーション (1998)
育ち盛りの子どもなら古着もある
If you have growing kids, secondhand clothes are an option too.
うるさいぞ育ち盛りの悪者どもめ！
Quiet down, you growing little miscreants!
— いまを生きる (1989)
育ち盛りだうんと食え年は？
You're still growing, so eat up. How old are you?
育ち盛りの子供にはもっと多くの食物が必要だ。
Growing children need more food.