My girlfriend has the same problem. She puts the younger girl almost 3 to bed earlier and threatens the older 2 boy 8 and girl 6 with their lives (in love of course!) if they wake up the little one. They get ready in the bathroom so there is minimal noise/distractions when it is time for them to go to bed.
She always talks about how nice it is when her older ones put the little one to bed...she can buy a few minutes during bedtime to do other things. The older ones help the little one dress, brush her teeth (they fight over it!) and read her stories.
I have an only child. I envy her!