Fasting is only obligatory upon reaching puberty, so young children are not sinful for not fasting. However, the Salaf trained their children to fast once they were physically able, gradually accustoming them to it. Al-Rubayyi' bint Mu'awwidh reported that they would make their young ones fast and give them toys made of wool to distract them when they cried from hunger until the time to break the fast. Parents should therefore encourage children with gentleness and half-day fasts, never forcing a child in a way that harms them.
Evidence — the daleel
Sahih al-Bukhari 1960 ṢaḥīḥSahih Muslim 1136 Ṣaḥīḥ
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.