The income of the foreigner who filed applications on behalf of his children is insufficient. Can he/she submit documents confirming entitlement to benefits (such as the 800+)?

One-off social benefits, purpose-specific benefits, aids of social character, unemployment benefits, child-support benefits  - the so-called ‘800+’ or financial assistance for holders of the Pole's Card DO NOT constitute stable and regular sources of income. Financial means obtained from the aforementioned benefits are not taken into account in the calculation of income required to be granted a residence permit.