Did this begin with the new battery? If yes I’d take it back and tell them you can’t have this problem with kids in the van and have them consider the previous reply of a defective battery. And it’s possible you have a drain of power somewhere that you’re not aware of like a light left on in the back -glovebox?, a stuck relay/switch, or a small short. Diagnosing those could be minutes to hours. Until you find out why I’d keep tabs on it by having the battery tested and charged up frequently so you don’t get stranded with your kids.