i come from a large mexican family my little niece just speaks spanish, she just starte kinder and with a few months already she was speaking english sure its sounds broken but i was still astonished
That's great. I'm a native spaker, but from what I understand English is very hard to actually learn
maybe little kids just learn faster , she gets home and starts counting and saying the a, b ,cs in english 
They absolutely do. Kids are like sponged. It's been said that it's much easier for kids to learn multiple languages than adults