No you cannot put baby teeth back in a kids mouth.
Baby teeth fall out around age 6 to 7 years old and when that happens there are new teeth that are being grown to push through.
So the old baby teeth are falling out to make room for the new adult permanent teeth.
Even permanent adult teeth cannot be put back in once they fall out.
You can get dental implants though if you lose your adult teeth but dental implants are expensive.
Everyone has the baby teeth fall out eventually and that is normal and when they lose the baby teeth new adult teeth will be grown in.
If the baby teeth are lose enough they may be able to be pulled out easily but eventually the baby teeth will fall out on their own.