сестра́ [sʲɪˈstra] Audio file also here: https://en.m.wiktionary.org/wiki/%D1%81%D0%B5%D1%81%D1%82%D1%80%D0%B0
And btw, it's a pain learning the International Phonetic Alphabet but definitely worthwhile...
And since it's gs., no 'ё': [sʲɪˈstrɨ] https://en.m.wiktionary.org/wiki/%D1%81%D0%B5%D1%81%D1%82%D1%80%D1%8B#Russian
Sorry, I don't understand what you mean. My question was about the meaning of "boy" and "мальчик" in this context. For me (not a native speaker), a boy (and hence мальчик) is a male 10-20 years old, but this seems not to be the case here. Is "boy" also a way to indicate a male newborn ?