Can anyone tell me what these plants are

lemonjello

 

 

marshmello

First one, looks like creeping buttercup.

Dovefromabove

Yes, first one's Creeping Buttercup and the second one is one of the many Hawkbits or Hawkweed - can't tell which one without close examination - there are many and they're all quite similar.

Both plants are weeds - Creeping Buttercup is quite invasive and the Hawkbit-type plant will spread all over your garden by seeds like smaller dandelion clocks.  I'd pull them up if I were you, unless you're very fond of them.