DD1 is 3.5 and DD2 is almost 16m and they have never been to a sleepover. DD1 stayed at my ILs for one night when I delivered DD2; but that doesn't really count!
But, BIL has offered to take both girls for a sleepover while his girls are here. Dinner, movie night, etc. I think DD1 will LOVE that and will have so much fun! Hopefully we can coordinate our schedules. Because, hello, child free night!!!