Retirement tax questions

If the beneficiary is still a minor who is responsible for making sure the taxes are filed?  In this situation for example, the grandfather sets up an UTMA for the grandchild, the grandchild's parents are not involved, and there are taxable realized gains in the account but no one files a tax return.  Who would be responsible for filing that return and paying penalties and interest; the minor, the grandfather or the unaware parents?

 

Also, in this scenario would income over $2,200 be taxed at the parents rate or the grandfather's rate?