CH1: Hiruzen took a long puff of his pipe. He said, "To be able to seal a tailed beast, one must have his chakra coils not developed. In addition, one or more people must sacrifice his, her, or their lives for the sacrifice to the Shinigami. This process is extremely taxing on not only the sealer but the baby. The baby has the distinct possibility to break down because of the energy of another being. He or she could die and release the beast."
Hiruzen's brain is malfunctioning if he must not remember Mito or Kushina and that they weren't newborns when they became Jinchuuriki (Mito was around 20s or 30s and Kushina was around 10, maybe a year or 2 older), in addition to not knowing that Naruto's seal (the 8 Trigrams Seal) is almost exactly like Kushina's (and maybe Mito's) with slight differences (Kushina had an altered 8 Trigrams Seal from what I know, similar to Naruto's but also different).