They are using their tongue, mouth and lips to learn about objects
Your baby is now becoming more interested in their environment. They will want to know more about the texture and taste of objects. Their fine motor skills are developing, but at the moment they can't squeeze, poke and stroke items using individual fingers. So, they will take these objects to their mouth to explore using their tongue, mouth and lips, which are full of nerves that tell your baby about the temperature, surface texture and other qualities.[2]
Your baby moves their mouth, tongue and lips in ways that help them to explore. They can suck and lick objects using their mouths and move their jaws around them.[3]
Your baby will learn about people and objects by combining information from their senses. Now their vision is developing, they will be starting to use their vision and touch to help them to understand things.
When you see your baby looking at an object before they put it in their mouth, this is a step in their development as they link what they see and feel in order to understand something.
Let the hands and feet exploration begin!
Your baby will soon be putting their hands and feet in their mouth in order to explore them. You might see your baby grab their feet with their hands, and bring them closer to their mouth when playing, or even during nappy changes. They may also try to discover more about their hands by licking or sucking them.
As your baby’s control of their hands and fingers develops, they will use their fingers to explore toys and objects. Using their mouths to explore objects will continue for some time. They will also develop control of their vision and attention, and you might notice them looking for objects for a little longer before touching them or bringing them to their mouth.
References:
[1] Shankar, S., Robertson, B-A., & Bobier, W.R. (2007). Parent/Caregive Narrative: Vision Development (0 - 6 Months). In L.M. Phillips (Ed.), Handbook of language and literacy development: A Roadmap from 0 - 60 Months. [online], pp. 1 - 5. London, ON: Canadian Language and Literacy Research Network. Available at: Handbook of language and literacy development
[2] Noreen Iftikhar, MD . (2020). Baby Mouthing — AKA Why Do Babies Put Everything in Their Mouths?. Available: https://www.healthline.com/health/baby/baby-mouthing.
[3] Gotzke, C. & Sample Gosse, H. (2007). Parent Narrative: Language 4 - 6 Months. In L.M. Phillips (Ed.), Handbook of language and literacy development: A Roadmap from 0 - 60 Months. [online], pp. 1 - 8. London, ON: Canadian Language and Literacy Research Network. Available at: Handbook of language and literacy development