My mom is a baby sitter for 20+years she has never request a playpen or anything. At most a net bouncer rocker or a mattress or Yao lan (depends on what the parents want the baby to sleep in).
I may be wrong but I feel ur nanny is incapable or lazy. Putting baby in play pen so that she can do whatever she wants, cooking, talking or the phone, watching tv etc etc etc while only using eye power to watch baby "jailed" in the playpen.
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