At first glance, it looks like the same base stats as a standard unicorn, with slightly different SLAs.
Make 'em Medium, or even Small?
Replace animal summoning with summon nature's ally.
Charm person or mammal no longer exists in 3.5; do we want separate charm person and charm animal spells or just charm monster (the original description said four spells).
Treasure type is Xx2. In 2e treasure type X is any 2 potions. Do we just give it no treasure like a standard unicorn in 3e or just items?
Let's go with charm animal, charm person, summon nature's ally I-III.
I kind of like the idea of giving them items only treasure (and maybe Use Magic Device as a skill).
Faerie unicorns or faerie steeds are seldom seen. This is because they can blend into their backgrounds in a manner similar to a chameleon. They can do this at will, with results identical to a creature wearing a cloak of elvenkind.
Added to Homebrews.
Likening them to ponies suits me. Comparing war ponies to light warhorses, Str and Con are both slightly less, while Dex is unchanged. I lowered both Str and Con similarly. Natural armor is 2 lower, so I made that adjustment as well. Finally, unicorns are the same speed as horses, so I made the faerie unicorn the same speed as a pony.
Flat +5 bonus on Hide checks (like the 3.5 cloak) and/or a racial bonus on Hide checks in forest environs?
Basic stats seem good here, too.
The Hide bit sounds like an at will Su that gives them a Hide bonus (flat +5 is ok, like the cloak) and maybe Hide in Plain Sight.