Your sentence is very close, but it can be improved a little for clarity and grammar. The correct way to say it is:
"I take my twins out for an afternoon nap in a stroller."
Here's why:
- We usually use "nap" instead of "sleep" when talking about short rests during the day.
- "Afternoon nap" is a common phrase.
- Adding "an" before "afternoon nap" is important because we are talking about one nap.
- Everything else is fine: "I take my twins out" means you bring them outside, and "in a stroller" tells us how they are seated.
So, the improved sentence is: I take my twins out for an afternoon nap in a stroller.