1. Still a little sapling, just a sprout.
sapling: 树苗，年轻人
eg. A sapling needs pruning, a child discipline. 小树要砍， 小孩要管。
2. Still a little sapling, just a sprout.
sprout: 苗，萌芽，发芽，这里用来比喻年轻人
eg.
Tom has sprout a beard since we see him last.
汤姆长胡子了，我们上次见到他时还没长呢。
Wisdom is likely to sprout where there are happiness and suffering.
快乐与痛苦出现时，智慧就可能在那时生起。
3. To keep you safe and sound, dear.
safe and sound: 安然无恙
eg.
Come home safe and sound! 愿您平安健康归来。
He arrived in England safe and sound. 他安全到达英国。
4. Mother knows best.
know best: 最有权威，最了解
eg.
The fact is that doctors don't always know best.
事实上，医生不一定经常都知道得最清楚。
If you already know best how to do it, just do it yourself.
如果你们已经知道怎么做最好，那么你们自己做就行了。