It is considered superior to offer food for Brahmacharis; a grishasta as per the ordained stipulations should wait for a guest to serve food and then partake it after serving a guest. If such is the case, it is not wrong to serve food to Brahmacharis as it is considered a noble deed.
Those who have performed bharanyasam can do so but not particularly on a kumara shashti which is for a demi-god. Everything that is done has to be done for the pleasure of Bhagavan, not for any benefit.