John Gill Commentary Lamentations 2:19

"Arise, cry out in the night, at the beginning of the watches; Pour out thy heart like water before the face of the Lord: Lift up thy hands toward him for the life of thy young children, that faint for hunger at the head of every street." — Lamentations 2:19 (ASV)

Arise, cry out in the night
That is, O daughter of Zion, or congregation of Israel, as the Targum; who are addressed and called upon by the prophet to arise from their beds, and shake off their sleep, and sloth, and stupidity, and cry to God in the night season; and be earnest and importunate with him for help and assistance. Aben Ezra rightly observes, that the word used signifies a lifting up of the voice both in singing and in lamentation; here it is used in the latter sense; and denotes great vehemency and earnestness in crying unto God, arising from deep distress and sorrow, which prevents sleep.

in the beginning of the watches
either at the first of them; so Broughton renders it, "at the first watch"; which began at the time of going to bed: or at the beginning of each of them; for with the ancient Jews there were three of them; in later times four: or in the beginning of the morning watch, as the Targum; very early in the morning, before sun rising; as they are called upon to pray late at night, so betimes in the morning.

pour out your heart like water before the face of the Lord
Use the utmost freedom with him; tell him, in the fullest manner, your whole case, fit your complaints; unbosom yourself to him; keep nothing from him; speak out freely all your soul needs; do all this publicly, and in the most affectionate way and manner, your soul melted in floods of tears, under a sense of sin, and pressing evils for it. The Targum is, ``pour out as water the perverseness of your heart, and return by repentance, and pray in the house of the congregation (or synagogue) before the face of the Lord:''

lift up your hands towards him
in prayer, as the Targum adds; for this is a prayer gesture, as in (Lamentations 3:41) (1 Timothy 2:8) ;

for the life of your young children that faint for hunger in the top of
every street
Pray for them, that they might have food and sustenance, to preserve them alive; who, for want of it, were ready to swoon and die the public streets; in the top of them, where they met, and where was the greatest concourse of people, and yet none able to relieve them.