It's not on the toxic plants list (whew, what a relief! I've fed my chickens dandelions since they were about a week old and never occurred to me they might be toxic - I figured if we can eat them, they can, which of course I know is not always true - please nobody yell at me for that comment.)
Anyway, I've found my chickens really don't like the flowers much, it's the leaves they love. (Even the guineas like them.) I have dandelions in the garden like crazy, and I just pull the whole thing up (have to twist to get most of the root out) and throw them in the chicken pen when I get a handful. They fight for them.
Mine did eat some of the flowers as babies - I too assumed they'd like them more than the leaves, but as soon as they had a choice they preferred the leaves.
Remember to give them some grit if you feed anything besides prepared feed.