Custodian Account for a grant child with 1099B, can the grant parent file the tax return for the grand kid ?

If the income is less than $1,300 no return has to be filed. If more, the child has to file their own return. You can’t report that income on your return in any case. 

Thanks for the reply. I did not include my grandchild’s tax return in mine. I prepared his own return and it shows that he owes $56. So I thought may be I can just sign the return (John Doe by grandma doe), and  attach a check to send to IRS.  I wonder if I can do the same for his state return as well which is only $6. That way, I don’t have to send the return to his parent for their signature then mail. Just try to simplify things without owing the government any tax. Surely, it will be Ok, right? Can someone confirm it? Thx bunch!

Sign the child’s name and write “by (your name) and “grandfather”.