We had an disagreement, and he took my keys, The kids are at home with him... He sent me to my sisters house... he said that because I left I was "abandoning" my kids, (and I am screwed)but it is a school night and the school is across the street from our house... so... does he automatically get custody?

No. Are you getting divorced? Have you separated? Has he filed anything do you know? I don't quite see what's going on.

Not anything serious, just left tonight... he just scared me 'cause he said I "left"! (Tonight)He made me pack a bag and told me I (abandoned) them... then my sister said that because I left the kids there (at home)That I did!. I don't think so.. I know he will get them to school tomorrow. I will pick them up from school tomorrow and (hopefully) keep them for the weekend.. so now what??

No, he's trying to scare you. How would a court know why one parent stayed home while the other went to a relative's? The children were not alone. But you say nothing serious and then ask now what... we don't know without some clue from you.. you are free to go back to the marital home anytime you want, and if threatened or he changes the locks, you bring a cop back with you. What do you want to do? If nothing serious, then why are you staying away? If you think a divorce is on the horizon, start writing everything down (a list, dates mainly) and find a lawyer and start salting away any pennies you can, even though the combined assets and income will pay for the expenses. Go home and gather any little mementos and items you treasure that he might destroy or take (or stay home, as is your right). Don't say much to the children if young, try to keep the scary stuff out of it.

Either he is trying to intimidate you or he just has no clue about the law.

He can't force you out of the house. It is the marital home and you have an equal right to be there. If he physically threatened you, you call the police. But since you did leave, that is a moot point.

So the question is, as Joy indicated, what do you want to do now? You can see a lawyer today and file for divorce. You can return and try to reconcile.

You have not abandoned the children. If he files for divorce first the court is going to laugh at him claiming abandonment for you going to stay with your sister.

If you decide not to see a lawyer today, we need to know more about the situation.

As for you picking up the children from school, there is no custody/visitation issues until you go to court to establish them. He has an equal right to keep the children as you do. There is no such thing as automatic custody.