I think it's all in fun and you should lighten up. My sons and daughter got their nails painted at a young age because they wanted to, and they all grew up to be perfectly fine adults without a penchant for vanity. (yes, I'm your generation and I let my boys get their nails done, too).

Besides, your daughter might decide "never again" once the toddler gets through squirming and whining her way through such a long "sit down" in the nail salon.