you've already asked this question some days ago and I tried to give you a detailed answer. The German law doesn't give a possibility to give a person a residence permit for family reunion to children after the asylum case had beed lost. The Ausländerbehörde can use another legal instrument - the humanitarian rule in §25.5 Aufenthaltsgesetz (I explained it in my ealier answer to you). This residence permit can be issued without waiting (it is on discretion of the Ausländerbehörde) and it ought to be issued after 18 months with Duldung, in this case the Ausländerbehörde must have special reasons to reject it. In most cases the Ausländerbehörden decide to give this residence permit to people only after 18 months, as they can't reject it without reasons anymore. It is difficult to claim for this residence permit earlier as the decision is in their discretionary power.
So you can take Duldung and wait or you can try to get a residence permit because of good integration (§25b) which I discussed with you previously.