Do non-balighs get reward for good deeds?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
Yes, children will be rewarded for doing good deeds, whether they are mature or not, and this is according to all four imāms of fiqh.
It is reported from Ibn ʻAbbās raḍiAllāhu ʻanhu: "A woman lifted up a child and said, 'O Messenger of Allāh, will his ḥajj be counted?' He said, 'Yes, and you will be rewarded.'"
Abū al-ʻĀliyah al-Riyāḥi reported that ʻUmar raḍiAllāhu ʻanhu said: "The young child's good deeds will be recorded but his bad deeds will not be recorded."
Only Allah knows best
Written by Shaykh Umer Khan
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Marʻātu al-Mafātīḥ Sharḥu Mishkati al-Maṣābīḥ, 8/313
 Ṣaḥīḥ al-Bukhārī, ḥadīth 1336
 al-Tamhīd, 1/10