How To Get A Kitten To Eat From A Bottle?

I have two kittens that want to drink from a bottle. The bottle has milk in it, but they are too young for solid food. I tried putting them on the counter so they could see it and get closer, but when I put the nipple in their mouths, they wouldn’t open wide enough to get any of it down. Also, once you let go of them after giving them some milk or formula, do you have to hold onto their collar? They come running back immediately! Thanks for your help!