Expenses below kindergarten are qaulifying expenses.
You must pay for care so that you and your wife can work, or be a full time student, or be looking for work.
If your wife is a full time student (determined by the definition of full time according to the school she attends) then she is imputed $250 of income for each month in which she is a student. That defines the maximum expense eligible for the credit. In other words, if she is a full time student for 12 months, then you can take the credit on up to $3000 of qualifying expenses. But if she is only a full time student for 5 months, then the maximum amount of expenses eligible for the credit is $1250 (and the credit amount is between 20-30% of eligible expenses.)
If she is looking for work, you can use the credit, but the maximum amount of the credit depends on her earned income from working. That means that if she earns at least $3000, you can claim the maximum credit for the whole year even though she may have only worked for part of the year. But if she looks for work but never actually earns any money, you can't claim the credit.
