While four years old is a little young for formal guitar lessons, it's not too early to begin teaching your child musical concepts that will be important once they are old enough for guitar instruction at School of Rock. Your 4-year-old can participate in the Little Wing music program to learn fundamental concepts through fun, dynamic musical activities. 
On guitars that have them, these components and the wires that connect them allow the player to control some aspects of the sound like volume or tone using knobs, switches, or buttons. The most basic electronic control is a volume knob. Some guitars also have a tone-control knob, and some guitars with multiple pickups have pickup selector switches or knobs to determine which pickup(s) are activated. At their simplest, these consist of passive components, such as potentiometers and capacitors, but may also include specialized integrated circuits or other active components requiring batteries for power, for preamplification and signal processing, or even for electronic tuning. In many cases, the electronics have some sort of shielding to prevent pickup of external interference and noise.
Open tuning refers to a guitar tuned so that strumming the open strings produces a chord, typically a major chord. The base chord consists of at least 3 notes and may include all the strings or a subset. The tuning is named for the open chord, Open D, open G, and open A are popular tunings. All similar chords in the chromatic scale can then be played by barring a single fret.[16] Open tunings are common in blues and folk music,[17] and they are used in the playing of slide and bottleneck guitars.[16][18] Many musicians use open tunings when playing slide guitar.[17]
You need to place one finger on whatever fret you want to bar and hold it there over all of the strings on that fret. The rest of your fingers will act as the next finger down the line (second finger barring, so third finger will be your main finger, and so on). You can also buy a capo, so that you don't have to deal with the pain of the guitar's strings going against your fingers. The capo bars the frets for you. This also works with a ukulele.

F major. This is fairly similar to the C, but a little more difficult to play. Press the fourth string down at the third fret with your ring finger, the third string down at the second fret with your middle finger, and the first and second strings down at the first fret with your index. You just flatten your index finger down across the two strings; lower your thumb if you struggle. You don't play the fifth or sixth strings in this chord.

On the other hand, some chords are more difficult to play in a regular tuning than in standard tuning. It can be difficult to play conventional chords especially in augmented-fourths tuning and all-fifths tuning,[20] in which the large spacings require hand stretching. Some chords, which are conventional in folk music, are difficult to play even in all-fourths and major-thirds tunings, which do not require more hand-stretching than standard tuning.[21]

First, being able to learn directly from amazing artists like Paul Gilbert is incredible. He's a great teacher and has a way of explaining things that are easy to understand and replicate. The video format is also extraordinarily helpful; I've used other sites that use only written materials (usually .pdf format), and they are difficult to navigate. The feedback, though, is what really makes this website head and shoulders above the others (even the other video websites). When I record myself and send it in, I get a response from Paul that critiques in an incredibly constructive way as well as additional exercises to work at really honing that skill. In addition, getting to see what tips he gave to other users is awesome! If you want to learn an instrument, there's no better way.
Peterson, Jonathon (2002). "Tuning in thirds: A new approach to playing leads to a new kind of guitar". American Lutherie: The Quarterly Journal of the Guild of American Luthiers. 8222 South Park Avenue, Tacoma WA 98408: USA.: The Guild of American Luthiers. 72 (Winter): 36–43. ISSN 1041-7176. Archived from the original on 21 October 2011. Retrieved 9 October 2012.
With so much information online about guitar theory, how do you know which sites to trust? Guitar teacher Zachary A. shares his top 10 favorite sites for learning about the guitar... Online resources for guitar theory are extremely helpful. You may want to explore the endless limits of the guitar, or maybe you're in need of a tiny refresher before your next lesson with a private teacher.  These 10 websites are all tremendously helpful tools for guitar players of all levels - beginner, interm
There really isn't a best age for kids to start guitar lessons, but most children under the age of 7 generally don't have the dexterity or patience needed to learn to play the guitar. With persistence and motivation some kids have learned to play guitar at some impressively young ages, but it really comes down to is the individual attitude and maturity level of the student. 
This unique degree program combines contemporary music performance training with the rigorous study of traditional disciplines including sight-reading, music history, arranging, conducting, recording and more. The comprehensive program instructs students to demonstrate stylistic depth, creative maturity and professional competence in preparation for careers in today’s music industry.