Not an English native speaker, but I would say that "talk" should work here as well as "speak"? I think it's usual to say "Can s/he talk?" in English
In this context, talk or speak is equally correct in English. (American nativespeaker.)
there should be some changes in the system with verb "osata" as its to "know how" basically, but in DUO used as know/can in different exercises and it supposed to be right both ways you write. But no.
Agree, it is very confusing. You could more accurately say 'Does the child know how to speak/talk'