transit on Beijing International airport

My son and I will be travelling thru Air China from manila 6:20 am arrived in beijing Airport at 11:am on February 23 and Travelling again at 7:40 am with China airlines going to Houston International airport we have lay over for 21 hours. My question do i need to check out my lugagge and check in on the next flight.. Is we are allowed to stay in the Beijing Airport for 21 hours lay over..