Girls help............?!?!?!?!?!?

ok so im going to spend the weekend with my neighbors in there new apartment and i got my period yesterday. well i just found out they want to go in the pool and i cant go in.(i hate tampons so im not gunna wear them.) well i cant make up an excuse cuz my older sister is going and i cant say i forgot my bathing suit cuz the mom of my neigbours will say borrow mine or ill buy u one. the thing is i could tell the mom cuz were close but the kids are like 8 yrs old and theyll keep asking to go in and so will the husband so idk what to do?? i was thinking of saying my friends wanna hang out tommorrow together for a barbeque but i kno theyll say ok well drop u off after!! so what do i do??