The fungus you observe in your mulch bears the indelicate common name 'dog vomit fungus'.  The spores were in the wood chips before the wood ever left the forest and has been lying dormant in your mulch waiting for the ideal conditions to display its 'fruiting body'.  The cool, damp spring we have experienced prompted the fungal display.  The fungus is harmless, but it would be appropriate for you to remove it and dispose of it. 
LS