I know it's used for child pornography, carding and malware related incomes but not for child slavery.

From the little I saw on underground forums LR is used for mid to low criminal incomes, by the like of botnet herding profits and carding infos trade. For things bigger and riskier like cashing out massive amounts of stolen cards and bank drops it's my understanding that cybercrooks are using money mule schemes and networks of off shore companies, not LR or similar... I'd flag child slavery as an high risk activity which can't be done just trough LR-like currencies, that's why I was asking for some sources.