You can only file I-130 now and wait for a visa quota.
Once available, the NVC will notify either the applicant, the sponsor, or the agent on file.
1. If the child will be still under 21 years old after 2 years, the child will be still under F2A. In that case, in order to adjust the status, the child must have a valid non-immigrant long-term visa in order to stay in the U.S.
2. If #1 above does not apply, the child will be eventually under F2B. The current wait time is about 7 years. There is no way a non-immigrant visa can last that long. In that case, the child is most likely to file the application in Taiwan.
3. A downgrade (F2A>F2B) is not automatic. You must notify NVC to confirm the change.
4. In all cases, the immigrant sponsor must maintain his/her residence as required by the law in order to maintain the sponsorship. Also, the child must remain single at all times. Once married, the child automatically loses the eligibility.