You raise a number of controversial questions about the relationship of language and thought and the possession of thought by non-adult humans and non-humans. You suggest that babies and animals can think. Do you think babies at any age can think, or just babies who have reached a certain level of cognitive maturity? Do you think all animals can think, or just some? Do oysters think? It appears that you attribute thinking to any organism that can sense. But most philosophers think that there is a distinction to be made between sensation and thought. An organism may be able to feel pain, for example, when it has certain unfortunate interactions with its environment. But it doesn't follow that that such an organism is thinking about it's environment. The sensation isn't a thought or a representation of the environment, but just a feeling caused by the environmental stimulus. This is a difficult philosophical distinction, one which has exercised many a great philosopher, and there's good reason to think that many philosophers were not as aware of the distinction as they should have been. So you're in good company!

Plants are caused to be in various states in response to environmental stimuli, but it's not clear that we should even attribute sensation to them. It's difficult to say what it is to have sensations, and to demonstrate that certain things, such as rocks and plants don't have them, we certainly wouldn't want to attribute sensations to anything that is caused to change its states in response to its interactions with its environment. A rusting piece of metal has not sensed the humidity which caused it to rust. A plant's flowers may open in the sunlight, but it may not be correct to say that the plant senses the sunlight.

We haven't addressed the issue of language and thought, which seems to have motivated your other questions. Here too, we can benefit from trying to be a bit more precise. What constitutes a language? You come close to suggesting that babies and other animals have a non-verbal language. It's true that young babies and other animals communicate without words, and they do so selectively in response to their environments. But we might want to resist characterizing such vocalizations as linguistic, pending an account of what contstitutes a language.

It is true that many types of things are repond in systematically recognizable and conistent ways to changes in their environment: including people, other animals, other types of organisms like plants, other living things like cells, and indeed non-living things like thermometers.

Philosophers have paid some attention to ways that things like these are sensitive to their environment. To consider the final example, on one epistemological line it is right to say that thermometers represent the temperature because they are sensitive in this manner to changes in temperature. I don't think this position is tantamount to saying that thermometers think, but I'll leave it to partisans of that perspective to say more.

One idea that rings true to me comes from the great 20th Century American philosoher Wilfrid Sellars, who drew a distinction between being "senstitive" to one's environment and being "aware" of it. In particular, it seems right to me to conclude that sensitivity plants and cells and thermometers and newborn babies show to their environments, this sensitivity is very much unlike the ways that you and I think about the world, which is based on a richer form of awareness than those other things are capable of manifesting.

By itself, this distinction does not imply that thought requires language. However, Sellars develpoed this insight in that direction. Likewise, Donald Davidson--another important 20th Century American philosopher--developed interesting arguments along a similar line, and I think arguments from Stoical philosophers about the dinstinctive nature of the sort of thought that you and I can manifest are also worth taking seriously. So, it strikes me that there are rich lines of thought that suggest, first, that babies and non-human animals and plants don't think in the way that you and I do and, second, that the way we think is intricately bound up with our linguistic abilities.