actually both chicks are boys. this was shown in an earlier chapter when the mother tried to determine their sexes by holding them upside down.
Ah! You're right...~ Sorry for my mistakes... I've checked them already. Thank you, (❁´▽`❁)*✲゚*
http://www.mangago.me/read-manga/i_don_t_want_to_say_i_m_a_chicken/mf/338194/Ch3/pg-4/
His sister is so cute!!! "Gege really is worthy of being Gege... He already came up with an escape plan in such a short amount of time... Here I come!! Weeee~~" (๑´ლ`๑)フフ♡