I just posted this in your AIBU version, but I'll copy it here -
Toss a coin. It will come down heads or tails at 50:50.
Imagine heads=girl, tails=boy. Toss a coin 4 times, imagining a family of 4 children. Keep a note of the results.
Do it again. And again. Lots of times.
A lot of the time you will get 2 boys and 2 girls. Sometimes you will get 3:1 or 1:3. Less often (but it will still happen) you will get 4:0.
This is all you need to explain "why some people have all children of the same sex".
Feel free to repeat for families of only 2 children -1 in 4 of them will have two boys, 1 in 4 will have two girls, only 2 in 4 will have a mix
For 3 children -2 of 8 families will have all the same, 6 out of 8 will have a mix
It's really not rare for families to have all the same sex, without any need for an explanation beyond the ordinary randomness of life.