

Dear Astha,
You question is quite valid & I first of all appreciate your observation skill as well as curious nature.
See dear, growing of a new born baby into a adult is a complex process which involves many different chemical processes.
According to Law of conservation of mass, mass is neither created nor destroyed during physical & chemical changes.
Though we observe increase in the mass while the baby is growing but let me tell you that every chemical change taking place in the body of new born baby follows this Law of conservation of mass. But it is due to the net effect of all those chemical changes we observe increase in mass.
