I learned how to sew at 8 when I started 4-H. I remember sewing on the lines to get the feel of the machine and being told to sew 5/8" seams because that is what garments have.
The big bags are the big rage - that is what I would start a beginner w/ making.
I would be careful w/ the girls on the pajama pants because if the girls are not all avg size - then the pants are going to need altering. - if they're short or tall, crotch length will need to be shortened or lengthened. If they're butt is too big, it'll need to be altered. If they don't fit right, it'll be a disastrous..