How do you politely tell your kasambahay not to let your children watch the soap operas and trash television she loves to see?

You can set rules as soon as you hire them. Make it clear from the start that you allow your kids to watch certain programs only. You can even give her a list and the specific hours when your kids are allowed to watch, and tell her that aside from those TV programs, you no longer allow your kids to watch any other program.