Can we claim our grandson's childcare expense on our taxes since our son is a full-time student

If you paid a day care center, babysitter, summer camp, or other care provider to care for a qualifying child under age 13 or a disabled dependent of any age, you may qualify for a tax credit of up to 35 percent of qualifying expenses of $3,000 for one child or dependent, or up to $6,000 for two or more children or dependents.  

Qualifying Child:

• The child must be related to you. The child can be your son, daughter, stepchild, eligible foster child, brother, sister, half-brother, half-sister, stepbrother, stepsister, adopted child or an offspring of any of them.
• Your child must be under age 19 or, if a full-time student, under age 24. There is no age limit if your child is permanently and totally disabled.
• Your child must live with you for more than half the year, but several exceptions apply (ie. away at school).
• The child cannot provide more than half of his/her support.
• You must be the only person claiming the child
• The child must be a US citizen, resident alien, national, or resident of Mexico or Canada.
• The child cannot file a joint return with his or her spouse. 

Deducting Summer Camps and Day Care with the Child and Dependent Care Credit

If your grandson is a qualifying child of only your son, then only your son will take the expenses.