I've got a toddler who wanted some more chips. My mum was staying for dinner and she said "there's none left" to encourage him to eat more vegetables on his plate— there were a bunch left, which my son could have seen for himself if he'd looked carefully. I didn't make a deal of it at the time, but it annoyed me.
Lying to manipulate your child into desired behaviour seems bad to me. Parents who say "the batteries are dead" when they don't children to watch TV, it's just conflict avoidant and eventually erodes trust.
This isn't just about the chips, my mum tells constant inconsequential lies constantly. Pretending she's heard of something you're talking about, or that she's been to a place she hasn't. Never admitting ignorance, always wanting to seem informed. The upshot is, she gets on with every stranger she meets straight away, but I can't trust half the things she says.
YABU: white lies for social convenience are fine, everyone does it, or maybe it's fine when it's done to small children for an easy life.
YANBU: we should model being honest to children and we should avoid bullshitting