PF, as a Eastern European you must be used to the idea of working mums. Do you question why women work in your own country? You also must be used to children attending nursery from a young age. Do you question that too? If you do, you probably have all the answers by now.
Then you get on to how you hide computer usage at work. Perhaps some of these working mums are very eficient workers (maybe exactly because they have learnt to juggle everything) and they don't have petty employers either. As long as the job is done why should anyone care what you do with your breaks? There will always be petty employers, whether of working mums or of au-pairs. I hope you also monitor computer usage of SAHMs, I'd hate to think SAHMs neglect their children to get on the computer.
Gee, innocently then talk about not wanting to upset anyone.