OK, since it would appear there are others out there who seem to have small hands, I'll let you know my vital statistics. They ARE tiny.
Measuring in the PALM SIDE of my hand:
From where hand joins wrist, to the very tip of middle finger is 157 mm
Little finger 47 mm long (or should that be short

).
A short little finger is classified as one whose length doesn't quite reach up to the third joint of the finger next to it.
Ok, now you can all go away and gasp at how small my hands are, how on earth do you play etc. etc. Don't worry, I've heard it all before but what I do get tired of is people treating me like a bit of freak because my hands are what they call, "dolly sized".
One thing I will say is that I CAN use my fourth finger and do. It is a total myth to say that you can't use your little finger because you have small hands etc. It is all down to rotation of the hand and building up strength and stamina in the hand muscles.
Remember, I started playing the violin when I was 10 years old when my joints were very supple. If I had started when I was in my late 20's for example, I may have had problems initially, but with regular practice the hands will loosen up - so no excuses from adult learners please.
Using the fourth finger high up on any of the strings is difficult (if not impossible!) for me, but there are always alternative fingerings and most players with small(ish) hands will invariably devise fingerings that exploit the use of just the first three fingers for the very high positions on all four strings.
ADVICE: If you do have hands as small as mine, or even smaller, then you will most certainly need a 7/8th sized violin. Most 4/4 violins will have a back length of 356 mm or more and probably quite wide shoulders. Avoid instruments with wide shoulders - small hands, short little finger in third position trying to reach the G string can be sheer agony. Look for violins that have smaller back lengths (350 mm or even slightly less), and thin necks, as this eases the stretch across the fingerboard on the G string. Violins with either flat shoulders or narrow shoulders are essential. Many old (c. 200 years) English instruments will suit small-handed players. Modern instruments of this size can be difficult to find, but shop around, they are out there.
EDIT: I can stretch (just) an octave on the piano, but no hope of playing any notes in between! I can manage a 15" backed viola - the stretches aren't as big between the notes as you might expect, but again, the neck if the viola is quite slim. The cello I play is a full-size genuine 18th century baroque instrument - except that in todays terms it would be classified as a 3/4 size. And finally, the oboes I play are professional Gillett system, closed hole, made by Howarth.