I think I would tell her at pick up the amount she owes you and tell her you need it paid tomorrow. I woukd also have a letter outlining this as well. If she shows up tomorrow without full payment I would not accept the kids into care. Also notify her that fees will now be paid in advance .... No pay no stay.... Inform her that failure to pay will result in legal action. If she shows up with partial payment take it ... But don't take the kids ..... No point going further into debt .... How would she like it if at the end of the week her boss said "oh sorry I don't have the money to pay you"?