Maybe this would be the case for another preposition, "Поговори с тем мальчиком"
Duo and some native-speakers have made it clear that это means "this" or "that", and that тo is used for "that" much less frequently, usually in somewhat special instances, more like "that (over there)"
You use тот in specific cases of pointing someone or something out who/which is not near you. Этот functions as both "this" or "that" is in a lot of circumstances
Shady_Arc said that:
"When pointing at a distant object you can use вон тот but it often awkward to refer to it as simply тот. We only use "это" to present an object ("Это её ноутбук")—outside poetry, at least.
Тот is quite popular in grammatical uses to connect clauses. You cannot replace it with этот in this use. The structure is similar to the formal and old-fashioned English "that which".
Это то, что я просил?. = Is this what I asked for?
Скажи тем, кто не придёт, что они уволены. = Tell those who do not come that they are fired.
То, о чём мы вчера говорили, крайне важно. = What we talked about yesterday is extremely important (lit. That about which we talked )
The same goes if you need то as an adjectival modifier when expressing "the one that...", though you may live without it (negation, though, makes it trickier):
Это не тот художни
Adding 'те' is the formal way of saying it. As it's instrumental (talk!), we use the perfective поговори(те) instead of the imperfective говори(те) if I am not mistaken.
Is dative also suited for this sentence or for говорить in general? Like "Поговори этому мальчику”?
Nay. There is something missing. You can rarely use "Поговори" without conjunction like "Поговори c X" or "Поговори про Y". And those rare occasions are basically short call-downs or remarks like "Поговори мне тут!", and they are certainly not in the field of basic learning course. Also, about dative. You can say smth like "Скажи этому мальчику", but it's expected from you to finish the sentence with something specific, like "Скажи этому мальчику про наш мяч". So, in the short sentences like "Talk to this boy", in Russian, it's basically ablative. Talk to whom? to this boy // Поговори с кем? с этим мальчиком.