We went straight to twins with my first 2, my third has a toddler bed, but only because there all in one room, and it takes up less space. I would just go with a twin.
I never bought a toddler bed. It seemed like a waste of money and by the time they used them, they were already able to climb in and out of our bed anyway. So around 2 they go straight to twin.
my daughter sleeps in a pay pen. but shes starting to be able to climb out. she's only one.
My two boys went from a crib straight to a twin bed. They were both around 2 1/2 years old. My little girls crib turns into a toddler bed so we'll probably do that first.