The first 20 minutes of every work day should be spent surfing the web looking for ridiculous things.... so i took it upon myself to google the crap out of this for you. I'm usually very good at this - I tried everything - "white mushroom brown center" "mushroom brown gooey center" and every description i could including all families of fungus and slime molds in case its not a mushroom. I had to sift through pictures of peoples fungal toes on google images looking for this.... and still NOTHING. Ok more coffee time i'll give it another 5 minutes of searching...

Alright, here we go - after reverse image searching your picture into google, and it taking me to a Dutch mushroom fan site .... I think its this -

https://g.co/kgs/sBgq9n 

Gloeophyllum odoratum

They are the fruiting bodies (mushrooms) from one of the zillions of fungal organisms that live in the soil and feed off of decaying organic matter....like old tree roots. They are harmless to the lawn and are very seasonal, usually appearing in late spring or early fall when temps are cool and rainfall plentiful. They will disappear on their own.

If a concern with your dogs, just rake them off and dispose of them. My own dog won't go near a mushroom!! Even a cooked edible one.

Where do you live?

What is your watering schedule? How often and for how long do you water?

Have you had much rain recently?