UTMA, 9yo grandchild, file taxes?

[Patti17]

I set up an UTMA for our grandson, now 9yo, with contributions going in automatically.  Do I file a tax return?  Is it included on our joint account?  How do I do the contributions, the interest and dividends, and the capital gains?

[Bsch4477]

I assume that any tax forms have his social security number. Whether he needs to file depends on how much he earned.