Traveling with one year old

Hi guys! I’ve traveled with my daughter many times as an infant, but this is our first time traveling with her as a toddler- it feels like a whole new adventure. Now that she does not fit in her infant carrier, what do we do about car seats? She is still only one so she will be on our lap and does not have a seat. But she needs her car seat for our destination. Do we check it as a bag? And if so, does it need to be packed in anything? Or can they put it under the plane like they do with our stroller? Thanks for your help!