Relevant Ability Score Bonuses
Shadowcasters use Intelligence and Charisma, and Children of the Night favor Dexterity. Shadowcasters don’t exactly hate Dex, for that matter, and of course no one wants to skimp on Constitution. Just things to keep in mind; not a lot of races have much more to offer than some ability score bonuses.
Unfortunately, bonuses to Charisma are extremely rare: the Spellscale (Races of the Dragon) and Spirit-mode Hellbred (Fiendish Codex II) have it, but both of those have −2 to Constitution, which hurts quite a lot. The only other LA +0 option is the “lesser” Aasimar from Player’s Guide to Faerûn, which has +2 Wisdom and +2 Charisma, but the race is pretty obviously not balanced and will likely be banned.
Bonuses to Intelligence are, unfortunately, not much more common; mostly a bunch of Elf subraces. Elf subraces are problematic because the overwhelming majority of them have −2 Constitution. Quick list of +Int elves: Gray Elf (Monster Manual or SRD), Fire Elf (Unearthed Arcana or SRD), and Sun Elf (Forgotten Realms Campaign Setting); all three get +2 Int and −2 Con (among other things).
“Lesser” Air, Earth, and Fire Genasi, as well as Tieflings (all Player’s Guide to Faerûn), also get +2 Int, but they all take −2 Cha so they’re a wash.
Better Intelligence-boosting races are all setting-specific, though. The Tinker Gnome (Dragonlance Campaign Setting) is actually quite solid, but it’s Dragonlance material, which many people have a pretty dim view of, balance-wise. The Deep Imaskari (Underdark) is from Forgotten Realms, which see quite a bit more play.
From Core races, Halflings and Gnomes aren’t bad; Dex and Con are not your primary scores but you like them, neither penalizes Int or Cha, and Small size is an advantage for you. Gnomes even have that aptitude for Illusion magic going on. But there are other considerations...
The obvious and immediate exception to the “races are only good for ability score bonuses” is the Human. A Bonus Feat is a really good feature. Humans are in the top three choices for race for almost every class in the game; Shadowcasters are in no way an exception to this.
Since you’re favoring sneaky types, the Strongheart Halfling (Forgotten Realms Campaign Setting) is even better: you’re basically a Small-sized Human. A lot of DMs won’t allow it though, for exactly that reason. Plus, it is setting-specific. But if you can, it’s a good choice. Other races that get a bonus feat (Silverbrow Humans from Dragon Magic, Azurin from Magic of Incarnum, etc.) are also good choices.
The Ultimate Sneak
But for your purposes, I’m thinking the Whisper Gnome (Races of Stone, or here) is an absolutely incredible choice. They are the sneaks par excellence. The −2 Charisma does definitely hurt, but you’ve got a huge array of bonuses there.
A Variant Kobold is a really respectable race (remember how Small size was an advantage? Welcome to doubling most of those advantages!). With the Dragonwrought feat (Races of the Dragon), however, it becomes a monstrosity. You see, Dragonwrought Kobolds do not get penalties to their physical scores when they age. As a result, a Dragonwrought Kobold who is Venerable has +3 to Int, Wis, and Cha, and no penalties from that aging. It’s a very, very high-optimization game where this should even be considered. Note that Dragonwrought Kobolds have all kinds of other cheesy tricks associated with them.
Bonuses to your most-important ability scores are too rare and costly because they’re basically all paired with −2 Con, so I would not bother with that. The exceptions there are the Deep Imaskari and Tinker Gnome, if you’re allowed them.
Small size is an advantage, so it might be better to just get a Small race you like. Halflings and Gnomes are decent; Strongheart Halflings, Whisper Gnomes, and (non-Venerable) variant Kobolds are great.
Humans, and other Human variants who share the Bonus Feat, are always good choices.
The “lesser” Aasimar is “too good,” though not as cheesy as the Venerable Dragonwrought Kobold, which is just insane.
Just in case it crossed your mind, there are no relevant LA +1-or-more races that are worthwhile to you from an optimization perspective. If you really feel like it, the Half-giant (Expanded Psionics Handbook or SRD) with the Primordial Giant template (Secrets of Xen’drik) has great ability score bonuses for you, but it’s still not worth the LA +1, and is another setting-specific thing.