Too many baby zombies

I was out killing some mobs for resources at night time, and suddenly I see a baby zombie. Then I see another... Then 2 more. Either I am really unlucky or there's a bug with zombie spawns.

 

All the baby zombies spawned in an area together. A few adults spawned with them too.

 

I am unable to provide a screenshot since I was fighting them off.

 

I have never seen so many zombies/baby zombies in one area before. I have not tried to see if it happens again, but I will check for more sometime.