Generally, both Yamaha and Cristofori teach music but Yamaha does it the unconventional way. I don't really know much about Cristofori because I have been in Yamaha since 4, and now still am
What Yamaha does is to put emphasis on playing by ear (hearing) and that is different in the sense that most other music schools start by teaching the techniques straightaway.
Yes, Yamaha does have its own set of courses catered for young (and old). The earliest is the Apple Course (I think for 2.5 or 3 years old, I can't remember) - so for those who are thinking of sending their son/daughter/nephew/niece for lessons at this young age, Apple Course will do fine.
For those who are a little late, they (referring to the young ones) can try the Yamaha Junior Course (YJC) - their age range is 4.5 to 5.5 years if I'm not wrong.
Hmm... Yamaha can start individual piano lessons at the age of 6, while Cristofori can do it at 5. It also depends on how fast the young ones can handle.
Cristofori follows the "conventional" track - Grade 1 ABRSM Theory, Practical, and then to Grade 2.... and the list goes on. However, Yamaha follows their own grading system and way.
Granted, you could also take Cristofori-styled lessons in Yamaha, but I would rather let the young ones experience a different system of learning. Both Cristofori's and Yamaha's methods have their own advantages and disadvantages.
For more information, you may check Yamaha's website (sg.yamaha.com) or Cristofori's one (I don't have it - I don't even know if Cristofori has a webpage)
But what I can say is that I feel Yamaha's system is much better than the conventional route. You can walk in and speak to the course coordinators/whoever that is experienced in the system to tell you guys more.
Yamaha also has its trademark specialisation in electronic organ (Electone). For those who are wondering what that is, it's a musical "monstrosity" (in a good way ) that consists of 2 keyboards and a pedalboard (YES that's equivalent to playing on the piano with your feet but let's not go into the nitty-gritty details of it shall we?), volume pedal and Pitch bend pedal (depending on the model), and a knee lever (to control sustain and solo lead voice)
It's good playing the Electone because you can apply each unique instrumental technique onto the keys. That said, if you want to play an orchestral piece, for example, your right hand needs to play and sound like a flute, left hand like trumpets, and feet like timpani. Not forgetting you may have to use the knee too or even use 2 feet on the pedalboard!
All the details if I were to list it out here for you, it would be very long and boring to read it all. So actually the best way to get information is through the website and previous "testimonials" (i.e. people who have experienced Yamaha and Cristofori separately) to see your needs and choices.
In my perspective,
If the end goal is just a leisure, non-serious lesson, choose Cristofori.
Other than that, Yamaha is much better.
I'm not being biased; I have experienced and seen both systems before - so I'm talking from experience.
Good luck in finding you and/or the young ones' passion in music!
If you have any questions, feel free to ask and I will try to give a reply as soon as possible.