If I leave my 3 children with my husband (who is verbally/physically abusive) and go to my mom’s and then file for child custody, would tht be consider abandonment?

It is not necessarily abandonment by itself, but it is a factor that the court can and will take into consideration when deciding custody.  Your husband's argument will be "if I was so verbally and physically abusive, then why would she leave the kids with me?"  This argument can and has worked before some judges who will discredit your testimony and abuse allegations.  The final decision for temporary orders will be up to the judge.  The judge could also see that you didn't have many choices and give the children back to you.  The judge could also find that you left the kids in an abusive situation and were not competent to protect your children-- and make a referral to the state children's protective agency.

 Instead of risking this, the better course of action would be to take the kids with you.  Many abusive husbands tell their wives that if they take the kids, they will have them arrested for kidnapping..... however, it's not against the law to take your own kids unless it's in violation of a court order.  If your mom does not have the resources to help you and your children, have her help you locate a woman's shelter in your area.  Call the clerk's office, call the police department, call local churches, google the internet.... one of them will know of a program in your area to help you get out, get safe, and possibly help with legal services for a protective order for you and your children.  The safety of you and your children are paramount and courts will respect that.  Leaving the kids behind in this situation is likely to subject them to his wrath for you leaving.  So do what you can to take them with you and avoid any abandonment allegations.