I did a bit of research because I'm used to seeing に as the subject of the passive sentence too (therefore I was inclined to agree with you), but my dictionary plays a slightly different tune than what I imagined:
子供に甘い be indulgent to (one's) children
子供に甘える to spoil (one's) children
甘えっこ spoilt child
犬などが人にじゃれつく (synonym) dogs are playful towards people
子供が親に甘える children nestle up to their parents
お言葉に甘えさせていただきます (I) will defer/depend to your words
It seems like the subject が/は babies/depends on/spoils the object に.
It's been a while since I dug around in the dictionary. It was a good exercise, thank you for providing me with the opportunity.
you are correct that に is use often with the passive voice. but in actuality に indicates direction.
in japanese は always marks the subject,not に, its just that the subject is often omitted from the sentence as its assumed from context you know who the subject is. (generally the subject is only included if the subject is new person/item from the previous sentence) and the object is often marked with a が or を
here the subject is 私、the object is ペン and the verb is give. and the person yo uare giving is is marked by に。 so i wil give this pen, to that person.
its the same with passive voice
私はその人にペンをもらった so i recieved a pen to that person (or i received a pen from that person, to make it sound less silly) in japanese they only use にto indicate direction and the verb tells us which direction. 私は鳥を食べた （I ate a bird） 私は鳥に食べられた （I was eaten to a bird or i was eaten by a bird) (食べられるis the passive form of 食べる）
so the verb 甘える mean to spoil, but dependant on the direction can also mean to be spoiled. active voice requires a を, whereas passive does not.
so 子供に甘える mean to be spoiled by you children as its (私は）子供に甘える (no を mean passive generally)
私は子供に甘い(です・である) does infact mean i am lenient on my children, but that is because 甘いis an adjective and not a verb. in this cause the verb is isto be'
thus （私は）TTKに甘える means i am spoilt by TTk, as with out the を to indicate the active voice its automatically a passive verb.
To say you spoil the TTK you must say （私は）TTKを甘える
I hope this explains things for you. as confusing and conveluded as my explaination is
not to sound arrogant but i am quite confident what i wrote is correct. I am a translator by trade and currently work for the japanese govt. lol well, for the board of education in a small country town.
anyway. i hope you continue to study japanese, its a very interesting language as it is so fundimentally different to english. lol whic his also why it is notorious for being difficult to learn from english. either way keep up the good work
I've recently graduated (my major were English and Japanese) and that's why I didn't dare to correct you. I wasn't sure. (I'm currently working on the furniture page as an exercise).
Anyway, I wasn't 100% positive that I got the correct meaning down, so I did my research and asked a Japanese friend in Facebook. She replied a few days later I posted here and, well, basically she wrote a summary of what you wrote here, but more confusing (Don't blame her though I know how confusing Japanese can be).
I thought about deleting my comment but I was curious about your answer. Thank you for taking the time to reply so in depth by the way and thank you for the encouragement!
no problem. im glad it was helpful. im on this page pretty often so if you have anyquestions im happy to help (provided im not busy with life/work etc)
there is nothing wrong with challenging something. thats how we learn, its better to ask questions than to blindly accept everything we are told. besides if nothign else it will be easier to rememeber if you learn something this way than just reading it in a book.
anyway. Have a nice day
Incidentally i also majored in japanese. so i know how confusing things can be trying to learn another language at college then you generally dont have nayone else other than your teacher to talk/discuss with