If your income is below the limit of €600/€900 gross per month, you can apply for Hartz IV at the Jobcentre. It can still happen that the income is up to €100 below the limit for exercising the right to Kinderzuschlag, then you can use the extended Kinderzuschlag approach. This option is better, because you don’t have to use the Jobcentre service. The problem with Jobcentre is the extensive application and documentation you need to submit.