All babies around 2 – 3 months, start to discover their own hands, play with them, touch and explore. At the same time put them in the mouth, taste – that calms them down. This is cognition (psychomotor development), and in order to get to know something all have to go to your mouth first :)) but little ones not only want to taste their hands, but also toys, mom’s/dad’s fingers. And later, they will try to catch their feet and put them to the mouth also, which is certainly not to be forbidden. These are the stages of cognition and the little ones have to do it.
Their meaning:
• when the baby puts his hand in his/her mouth, he/she becomes aware of their own hands and their possibilities 
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• putting their feet in a mouth – as well this is letting to know the lower limbs, and it’s one of the signs the the baby will be ready to sit down soon 
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But if he/she sucks his/her thumb? What to do then?
Hand thumbs babies where already sucking in the uterus. Also drank the amniotic fluid (water) in the tummy
. You shouldn’t have to worry too much if those sucking are mostly rare. But if the baby is doing it on a regular basis, it should be prevented, as it can be difficult to wean from that later. Because of actively sucking the thumb, the reflex (born sucking reflex) can be done with pleasure. Instead try to put a toy in the hand, or a chewing toy, or give a hug, or put a special glove, letting to suck a pacifier should be the last thing you do. There are a lot of different opinions about the pacifier, but I will write about it in another post. 
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What can happen if the baby is constantly sucking his/her thumb?
The thumb is often in the mouth (a wet environment), the skin of the finger and the nail may become thin, and the nail itself can change. 
It is also important to know that, while your finger is constantly in your mouth, the stomach shrinks, producing more digestive juices than it’s needed, which can cause abdominal pain. 
Also, the upper jaw may narrow and the teeth occlusion can change. For some children, this habit may last for years and more, so you should try to prevent this habit from happening by being noticed in a timely manner. 
I remember that I have to see an older girl (2-3 years old) still sucking her thumb, and myself I remember for a long time I was chewing my nails. This can possibly happen with excitement, greater or less stress – if a child wants to calm down or cope with their emotions, the finger can move instinctively into the mouth. 
For older children this should not be a demand that their finger needs to be removed from the mouth.
You need to analize why it is happening:
• Where it takes place?
• When does a child do it?
• What time of a day?
• How does he/she feel?
• What are the people who is he/she surrounded by?
• What topic was talked about when it happened?
Try just to talk to your child, hug, answer, ask for help, say that you love him/her, because feeling safe is the most important moment for the child when they are showing emotions 
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