From the instruction for child care tax credit:
"The care must have been provided so you – and your spouse if you are
married filing jointly – could work or look for work."
It doesn't matter if it's preschool or daycare or kindergarten after-school.
What matters is that the costs enabled your wife to work or actively look
for work. If your wife has simply been staying at home, then you can't claim
the credit. I don't know what IRS's definition is about "look for work".
But if your wife hasn't worked for quite a while, it will raise some red
flags and you should probably try to find some proof to show that she had
been trying to find a job--just in case you get audited. Better be honest
than sorry.