Is it just my games or does it seem that it gets harder and harder to have kids with each new generation?

I had NO problems getting to 6 kids with the first few generations and now (4-5) generation I find it is hard to even have 3!

"We" keep trying but it seems that even with all the jumping around there is no stork. And 'we' get a lot more "Arguing" than before?

I have tried to pass on the house to Defenitly or Would be nice couples and it doesn't seem to help.