New Portrait Painting

I've begun to draw up my next portrait painting of the grandkids.  Since the last one was finished, I have two more kids to add to the picture!

This is a rough sketch of the composition on an A4 piece of paper, taken from a photo shoot I did one afternoon with the kids.  I took about 200 photos in all and picked out the best of some of them.  I'm in the middle of re-drawing the composition on to my canvas which is a fairly large 101 x 76 cm.