For me, there is no such thing as too early to start especially when it comes to music. As much as for my children to learn something new while they are still young, a parent can only give them support and motivation in order for them to get into learning music. I bought each of my girls a ukelele when we went on a vacation to my home country two years ago but they seemed like they have forgotten those cute little things already simply because mommy got busy and did not get in their behinds to at least push them to watch video tutorials for guitar lessons.
That is our case in this family. Seems like my children have different interests than music. If yours are into it, please encourage them to continue what they’re doing because it is just so amazing for a child or someone who can sings or plays a musical instrument. If you are looking for to start with, search for ukulele for sale at musiciansfriend.com.