Here's my two cents as a player who played through this adventure twice:
--The hardest part of this adventure seems to be not boring your characters to tears early on. I saw this adventure run once by a mediocre DM and once by a much better one and that was the major difference. Keep things moving, and especially don't let things bog down when the player's need to find a secret entrance down.
Playing Rose and Thorne requires some subtlety. It seems like everyone's first instinct is to play up how creepy the children are, turning Rose into a sort of Wednesday Adams. I think the opposite strategy should be employed. The two children should be at least a little sympathetic, otherwise the whole adventure feels forced. Under the more mediocre DM, the whole group just wandered around listlessly because Rose and Thorne made the adventure feel like an obvious trap and no one really connected with it's premise.
-- Don't undersell the underlying story. When we came to the crib room, we fought a ghost. Under the second DM, we fought the maddened ghost of the former nursemaid. That difference is crucial. Without accentuating the flavor and mood of this adventure, this is actually a dull as dirt adventure.
