Work dilemma-- kids in gym care

I currently work at a gym in the child care section. Our job is basically to just sit with the kids while their parents work out, which is easy enough, but we can have up to 30 kids of varying ages with (at most) four employees- which again- is manageable. However, two of the girls I work with just sit and talk all night and leave me to watch all the kids. It's happened on multiple occasions and it's making me upset, not because I'm doing all the work, but because I'm worried for the kids. Me trying to watch 30 kids at once almost promises I'll miss something or someone could get hurt. The other girls are young and don't care though. One of them also is constantly on their phone in front of parents which makes us look bad as well. I want to tell my manager but she is upset with me (although I don't feel it justified) because my husband is a marine and I asked for time off to take leave with him which he only gets once a year, which will leave her short staffed, but I gave two months notice. I feel like telling her wouldn't solve anything but I'm worried for the kids. I've debated submitting a complaint through the website pretending to be a parent but I feel like that's cowardly too. I am not a confrontational people, and don't want a bad work environment or stress where I just found out I'm pregnant. I just don't know what to do :( advice?