Should my future children adhere to Sunni or Shia teachings since a Sunni boy wishes to marry me, although I identify as a Twelver Shia?
Your responsibility is to teach your children the real Islamic teachings of the Prophet Muhammad (SAWA) and his Ahlul Bayt (AS) and bring them up as sincere followers of the Prophet and his Progeny (AS). If you have a reasonable possibility that this marriage might harm your faith and religious practice, you should then avoid it. You faith in Allah, the Prophet and Ahlul Bayt (AS) is more important your sentiments and emotions.
Wassalam.