How do I do stop my 3 month old from sucking her thumb?

Personally, I think it's okay for a baby that young to suck her thumb. It's a reflex action and really natural. There are some advantages to a thumb sucking baby. With her thumb, your newborn has a built-in natural way to calm herself down any time she’s feeling cranky. If you're really uncomfortable with baby sucking her thumb, you can use a pacifier. I know my late grandmother had really old-school methods to stop me and my siblings from thumb sucking such as putting a spot of lemon juice on the thumbs but I wouldn't do that to my kids personally. As your child grows, too much thumb sucking may disturb the alignment of your child’s teeth and even the structure of her mouth, so you’ll definitely want to wean her off before her permanent front teeth come in, around age six. For now, I think it's okay :)

My 3 month old is a thumb sucker too. When I pull her finger out of her mouth, there's a loud "pop". I bought a pacifier for her but she's too used to the breast so she refused the pacifier as well. I don't mind that she sucks her thumb because it's always there when she needs it. As for weaning, she can self wean. Babies are really smart. If you don't want her to suck her thumb, I've seen how some parents tuck their child's arms into their pants so they can't suck their thumbs. Haha!

Agree with Idza. My son started stuffing his fingers at that age. Probably because he has just found his fingers; like how he just found his feet at 6 months and has been stuffing them too. But once they are older, and when they can understand and take instructions, that is when I will say no to them.

thanks