Has anyone ever use this earmuff for baby? I'm tempted to buy, just thinking if he can sleep/rest better in crowded places (malls, outdoor)? Or should i just live without it?

I would live without it. Babies can learn to sleep thru noise. The quieter environment we provide for them, the easier they woke up at the slightest noise. Unless you are thinking of going concert or places with very loud volume then this is necessary.