This is my second year teaching 1st grade CCD (I;ve taught other grades before) and while we use a different book, it is interesting to see what you are doing with your kids. I did discover last year that they learned the basic prayers really well simply by praying them. We use them as part of our opening prayers, along with reading a Bible verse and everyone saying someone they are praying for or something they are thankful for. We also pray one right as we are about to walk out the door. By the end of the year with only a little more focus on them, they all knew the Sign of the Cross, the Glory Be, the Our Father, and most knew the Hail Mary (it was the last one I introduced).
I have been saying the Our Father as our opening prayer every week, and we make the sign of the cross together every time we pray, even if we are about to pray silently. The "practice" activities that I'm giving at the beginning of class are mainly just to give one child something to do while we wait for the other to show up. (I only have 2 students.) I also have one student who speaks English as a second language, so having different practice activities for that child has been helpful in reinforcing the words that might be unfamiliar. We have had four classes now, and I think they do know the Sign of the Cross now. The textbook introduces the Our Father in a few more weeks, but I'll probably start explicitly working on it a little bit sooner since they seem ready.