This is irreplaceable.
The definition of irreplaceable is something or someone that cannot be replaced.
Your children are an example of something you would describe as irreplaceable.
Impossible to replace: irreplaceable antiques.
- ir′re·place′a·bil′i·ty, ir′re·place′a·ble·ness
(comparative more irreplaceable, superlative most irreplaceable)
- That cannot be replaced.
ir- + replaceable