I am just making a general observation. I have done much research on types of practice, brain development, etc. (By the way, I have 5 grown children - was one of the first to homeschool!!)
Try to get Noah (and the others too) to stop when he makes a mistake. Look at the music, look at the keys, consciously think about what he did, then start over and play correctly. Have him stop EVERY time he makes a mistake and either start over or back up a bit if he is well into the piece. If a mistake is make, corrected and one just goes on, the brain does not know which is "correct", the mistake or the corrected mistake, and it may take several times through before the song can be completely played correctly.
I am not just speaking of notes here, but also rhythm. Play small portions at a time to get the rhythm correct. Play until it is easy for the hands to move with correct rhythm.
Trust me, practicing like this promotes brain development and really it DOES take less time to learn a piece completely when practicing like this. This computer program is fantastic because it does indicate "mistakes". Once a piece is learned, it is really fun to play the piece with the computer!
If you can find a small rubber ball, have Maria hold it in her fingertips and squeeze it - one finger with her thumb at a time at first, then a couple fingers, then all her fingers. Keep all the knuckles bent - even the ones between the finger and hand. It one collapses, stop squeezing and start over. I found a ball about 1 1/2 or 2 inches in diameter that has little spikes all over it so it is easy to hold anywhere without the fingers slipping off, so works really well. It also lights up when bounced!
I am also a violinist and as a child with really small hands, this was an exercise that I had to do to strengthen my fingers in order to hold down the violin strings properly. After awhile, my mother referred to my fingers as "fingers of steel".
I am glad that Hellene mentioned playing two keys with a bent thumb. I was going to mention that as well, but then noticed the third chord - the C, F, A - that really is beyond Maria's reach I think. Sometimes - and this is something I had to do - you can reach a note by touching the key with the thumb on the front rather than from the top. I hope I am making sense.
Keep up the good work!!!!