Board Thread:Questions and Answers/@comment-25951143-20150101110046/@comment-26871067-20161002173819

My earlier suggestion that Alluka's prison is full of toys as a placating measure (and not an indication of what the Zoldycks actually believe about her) is directly supported (and almost directly stated, I'd even argue that he explicitly says it) by Killua in chapter 326 (page 5 of the chapter, for reference).

Killua says (and I should not it's not "I think that", he says it with the confidence that it is fact) that the disconnect between Alluka's strict confinement and room full of toys is because Silva is afraid of her powers, but he also wants to basically get on her good side in the hopes of controlling her (ability).