I think you see the whole thing totally wrong.
A direct object never has a preposition.
- I'm reading a novel - a novel is a direct object. You ask: What am I reading?
- I'm waiting for the bus - for the bus is a prepositional object You ask: What am I waiting for?
In your sentence "Pilgrims learned about planting crops from the Wampanoags."
"about planting crops" is a prepositional object
and
"from the Wampanoags" is a second prepositional object.
Maybe English grammars have other terms, but that's the way I see it.
It can be argued that with to tell, which is normally a bitransitive verb taking both sorts of objects as in to tell someone something, can exist with just an indirect object alone.
There is an unspoken “something” that is being alluded to here, and that thing unsaid is the direct object, with the person receiving the information being in the indirect object position.
However, this analysis is not universally accepted. Others view this particular situation as one where the indirect object has passed to a direct one. The OED seems to be one of these; the following citation is taken from its entry for the verb tell:
trans. to tell a person (the originally indirect or dative personal object becoming the direct).
Note the parenthetical portion. They have stopped calling it an indirect object there. It’s the only object in sight, so it “must” be a direct one. I guess.
In other languages that have stronger case systems, this sort of use can take an indirect object by itself, and when it does, it is still marked in the dative’s indirect object case. So for example, the Spanish for tell me it is dímelo; if you wanted to add and tell her too while you’re at it, you would have to say dile to mean “tell her” using the dative enclitic pronoun le. You cannot use the accusative enclitic pronoun la, because it is still indirect. So they in Spanish do not reanalyse the remaining object as a direct one. It stays dative in their minds. It is that line of reasoning that leaves it as an indirect object for some English grammarians, too.
Now, you can construct that same situation in English, but to do so you have to go back to when English was what for us today was a foreign language. A thousand years ago when English had a more robust case system, you sometimes had certain verbs that took only a dative case pronoun for their complement without an accusative case one to go along with it. So one could (perhaps) say they only took an indirect object. However, most of the time we translate those uses from Old English and dative objects into regular direct objects today so as not to confuse people.
However, one rare place where that still occurs is in the frozen relic verbs meseem and methink, once spelled me seems and me thinks (or me thought and so on). There the Old English dative me, which in those expressions came before the actual verb, became stuck when it fossilized. We no longer think of it as being an indirect object. But it really is an isolated dative, because it is the very sort of “to/for me” kind of “dative of interest” you find in modern expressions like cry me a river or sing me a song. So meseems just means it seems to me. That’s why the singular is meseems, as in Meseems unlikely that he shall pursue us meaning it seems unlikely to me.
But those are just curiosities from the museum case, not productive uses. If you abbreviate sing me a song to sing me, folks are going to think that use of me has switched to a direct object use from an indirect object one, and wonder what it is you really meant by that.
Best Answer
All of your examples are grammatically correct, so it's more a question of what sounds best, and what would be considered best style. Concerning style, there are a few general rules.
(1) If a direct object is a pronoun, then it is often preferable to express the indirect object with a prepositional phrase, placed after the direct object.
Consider the sentence, "I sent you it." Sounds awkward, doesn't it? It does at least to native speakers. This is likely due to cadence—the pronoun "it" doesn't like to be stressed. In cases like these, it's better to use the preposition. "I sent it to you." Now, that's better. However, I should add that there are exceptions to this rule. For example, "I sent you something" is a set phrase which sounds perfectly fine.
(2) Otherwise, if you wish to place the indirect object first, then you don't need the preposition.
If you place the indirect object before the direct object, then you may choose whether or not to use the preposition. It's usually best style not to use a preposition, as it normally sounds fine this way, and in general less is more. But if you choose to use the preposition, then it's still grammatically correct. It's more a question of style.