Why are there no roots when a child's baby tooth falls out?

When a baby's tooth erupts, the tooth has roots that hold on to the jawbone and tissues that hold on to the gums. Eruptions often happens at around 6 months of age. There are 20 baby or deciduous teeth and 32 adult teeth. When the child turns around 6 or 7 years of age, the deciduous teeth start to fall out and adult teeth start to arrive. 

So, given that deciduous teeth, like adult teeth have roots, parents might then be surprised to see no roots when a baby tooth falls out.  However, this is completely normal.

The process that happens when baby teeth grow out is called resorption. Resorption is when the body resorbs the dental tissue that connects the baby teeth to the gums and the roots so that the teeth can fall out.

Information source: https://www.colgate.com/en-us