CAULKING CRACKS IN CONCRETE

Prepare the cracked concrete by spraying herbicide (like Weed-Be-Gone) to kill weeds back to the roots.
Dig out all of the dirt, plant debris, and weeds from the cracks.  Then vacuum out the dirt.
Apply concrete sealant into the cracks.
The finished result.  This will prevent water from flowing under your paving and will prevent the paving slabs from settling any further.
An easy project and very satisfying.