Can the fit truly be universal?? My son is 4 and a half years old and is starting to play an 1/8 size cello. Will it fit him and his little bow?

I think it would depend on the diameter of the bow. If the diameter is the same as, say, a 4/4 bow, then yes I think it would fit as that is where it is the snuggest. On my 4/4 bow, it goes about 1.25" beyond the frog, so make sure there's enough room too.

Does this work for a small 3 year old? My 3 year old student plays a ciola (viola with endpin, held as a cello). A 1/10 size cello is too big for him

First, view image here: https://www.things4strings.com/images/easyblog_articles/325/b2ap3_thumbnail_CPage3TwoViews-compressed.jpg The bow provides the breath of tone for string players. While cello bow technique varies widely among fine players, all agree a primary focus of the cello bow hold is lack of tension, and a flexible thumb and fingers. The good news is that the CelloPhant® accessory instantly relaxes and supports the fingers of the bow hold! The various anatomical features of the elephant, such as toenails and legs, allow the cellist to feel reference points, for consistent bow holds from practice to practice. The size of the accessory allows an open, relaxed hand, and the circle of the elephant's trunk directs a flexible thumb toward the intersection of the frog and stick, with alternate placements if desired. Teachers appreciate the flexible-use design of this accessory, allowing for differences of pronation, depending on their own bow technique and student hand size. The accessory is useful for all hand sizes, age 3 through Adult. Teachers of very young cellists have discovered the special features Martha Brons designed in the accessory for the very youngest Suzuki cello students: an alternate thumb location is to roll thumb tip around elephant's cheek (or between cheek and ear); and young ring fingers like to rest on the top edge of the elephant's leg. Best tone results when the bow is rested on the string before the right hand is placed. The accessory also is designed to deliberately add a touch of weight to assist beginning players to achieve a bit more effortless tone -- more tone with which to fall in love!Invented by master string teachers, award-winning Things 4 Strings® bow accessories help shape and stabilize bow holds – moving beginning players to a functional bow hold in an Instant! The accessories uniquely train the hand to hold the bow correctly and naturally, through muscle memory, thereby freeing the player to learn and enjoy other elements of string playing.

Will this fit a twinkle bow and a 1/10 cello bow? Can a 3 year old use this?

Hi - yes, the CelloPhant will fit on a 1/10th and Twinkle bow. Please note that the Twinkle Bows are usually for violin, so the CelloPhant may fit a little looser than the 1/10th cello bow. From our blog post on this topic: "Teachers of very young cellists have discovered the special features Martha Brons designed in the accessory for the very youngest Suzuki cello students: an alternate thumb location is to roll thumb tip around elephant's cheek (or between cheek and ear); and young ring fingers like to rest on the top edge of the elephant's leg. Best tone results when the bow is rested on the string before the right hand is placed."