This 250,000 to 300,000 average per year is the bulk number....meaning each single individual (families included). There’s like three periods (the Balkans War period, the Yugoslav War period, and the 2014/2015 period) which are exceptions to the average.
Last year, some German university did a study which looked at the immigrants going back to the 1960s (all the Turks, Greeks, etc). It’s an odd analysis. On the 1st generation....they did go and have three to five kids. But as those kids grew up...they became Germanized, got married, and went to the German standard of 0, 1 or 2 kids. Logic explained is that cost of living in Germany makes having kids more difficult. Go look for a 3-bedroom apartment at a decent price....you won’t find it in major cities.
The study concluded that immigration doesn’t change much of anything because they all adapt and go back to the 1.5 standard.
Curious - What percentage of the population is practicing Muslim? Also, do kids of Muslims born in Germany tend to remain Muslims? When you say they become Germanized what does that mean religion-wise?