1- Celebrating Mawlid al-Nabi (Prophet Muhammad’s birthday) is an innovation. 2- Buying sweets on Mawlid al-Nabi comes under the heading of helping and propagating the celebration of Prophet Muhammad’s birthday; rather it is a kind of establishing that festival or ‘Eid. So it is better for you not to do that on the day of the celebration.

Celebrating the 15th of Sha’ban is not permissible whether that is by spending the night in prayer, dhikr and reading Quran, or by distributing sweets or giving food to people and so on. For more, please see the detailed answer.