When I was young, I learned and prayed before bed the prayer that begins “Now I lay me down to sleep. I pray the L-RD my soul to keep. . .” My kids learned it when they were small, too.
What prayer is there for adults? Try Psalm 3.
1 O L-RD, how many are my foes!
Many are rising against me;
2 many are saying of my soul,
“There is no salvation for him in G-D.” Selah
3 But you, O L-RD, are a shield about me,
my glory, and the lifter of my head.
4 I cried aloud to the L-RD,
and he answered me from his holy hill. Selah
5 I lay down and slept;
I woke again, for the Lord sustained me.
6 I will not be afraid of many thousands of people
who have set themselves against me all around.
7 Arise, O L-RD!
Save me, O my G-D!
For you strike all my enemies on the cheek;
you break the teeth of the wicked.
8 Salvation belongs to the Lord;
your blessing be on your people! Selah
The L-RD bless you and protect you!
The L-RD deal kindly and graciously with you!
The L-RD bestow His favor upon you and grant you peace!