If you receive maintenance payments for your children from the other parent, you must pay tax on these. This also applies to child allowances. But one-off payments, i.e. money that you receive in a lump sum for maintenance, are not taxable.
You only have to pay tax on the money until your child reaches the age of majority. If your child is of legal age, maintenance payments are treated differently and fall under different rules.
Even if you receive more alimony than was originally stipulated in the divorce or separation decree, you must pay tax on the entire amount. The person paying the maintenance can deduct this amount from their income.
If you receive maintenance payments, you are also entitled to a child deduction on your tax return for each child for whom you receive maintenance.