Tried tommie tippee, nuk, avent brands since about 3wks old. He's now 20wks. He just won't have it just looks confused and pushes it out. Tried when he's happy, tried when's he's crying. Tried BF him then slipping it in. Put a drip of calpol on the end of one for him to have some flavour. But he's not having any of it!