Learning something new brings potential excitement, uncertainty, challenge, risk, reward, and new opportunities for accomplishment as well as the possibility of stumbles along the way. After years of teaching, I have found that this venture into unknown of trying something new can veer into the territory of fear and shame for young people.
As parents and teachers, we see the big picture and we know that mixing up fingers in a new piece is not the end of the world. But to a young person who looks to adults in their life for validation and support, that mix up of fingers can be embarrassing and disappointing and probably scary. This is a great reminder to always be positive and encouraging of your brave young guitarists who are juggling multiple complex thoughts and motor skills to make music (see the One Point Lesson post). It's also a great time to employ depersonalization: a finger mix up is not because your young guitarist is not smart enough to figure this out! Fingers are stubborn and even when our brains tell them what to do, they do something else.
Very often in lessons I use depersonalizing language after hearing a student play a piece where fingers don't do what they're supposed to. Rather than say, "You forgot to hold down your 3 finger until 1 finger was ready. Do it again, and this time, remember to hold down 3 finger" I'll say, "3 finger forgot to hold down until 1 finger was ready, let's try that again and stop or slow down to make sure that 3 finger remembers this time." It's a very simple reframing to take the onus off the student and put it on the "fingers." It puts you and your student on the same team to remind the fingers of what they need to do. If fingers keep getting mixed up, it's much easier to laugh it off together and try again than if the blame is placed on the student who is then afraid to try it again out of fear of embarrassment or disappointment.
Remember that we, the adults, have the ability to make trying something new less scary by our words. Work hard, take responsibility together, but keep practice positive and you'll train adventurous and happy musicians!