Hi, 

Signs of fungal growth on the trunk of trees often mean the wood is decaying underneath, not from the fungus but as a secondary response. 

We would recommend contacting a certified arborist to examine if the tree is safe structurally. 

As long as no one is eating the fungal growth, they are most likely fine in those terms. If you happen to touch them with bare hands, just wash your hands afterwards. 

Emily