Don't worry about it. 6-7yrs is the time period for permanent lower 1st molar & front 2 teeth called as the central incisors. Also for cavity , clinical examination should be done, which requires some small radiograph for determining the extent of it. Depending upon the results of it further treatment will be carried out.

Get an X-ray done of the tooth which has cavity and the non erupting tooth bud... If the tooth with cavity is near exfoliation removal of tooth can be done with space maintainer unless permanent erupts and for the once which has fallen X-ray will till in how much time permanent will erupt

Cavity needs to be restored . Visit  a nearby dentist , get d cavity filled and also get an x ray done of the unerupted teeth  to get an overview of permanent tooth bud inside .