My helper wants to take a month off to return home for a visit, and I can't do without someone at home to look after the kids, anyone know of a good agency where I can engage in a temporary maid. How do they charge and what is the soonest I can get her to start?

You can refer to this article for some options that you can consider (between Babysitters and Nannies): http://blog.moneysmart.sg/family/childcare-options-in-singapore-which-one-should-you-choose-and-how-much-does-it-cost/ The last section also offers some links to agencies which provide such services. You can contact the respective agencies to find out about their availability.