If my parents pay for my college and they have invested in mutual funds, is it an obligation for me to look into whether it is halal or not, I find this issue extremely confusing, and so I would prefer just not to engage in it, however my parents have engaged in it.
Such concerns are indicative of a person's faith and yaqeen, may Allah keep such Iman alive inside you throughout your life.
Regarding your question, investing in mutual funds can be halal provided the conditions laid down by shariah are met. If it's halal investment, there's no need to worry. If they have invested in companies that deal in haram (like insurance, banks and liquor stores) then it needs to be seen if this is the primary source they are using to pay for your college fees. If this is not the main source and they have another halal source of income that they use primarily to pay your fees, it's fine for you to accept still.
The rule here is that a person is not allowed to benefit from even his parents if their income is all haram but if it's mixed income with half halal and half haram, you may accept this gift of college fee from them. So, advice for you is you find out about the shar'i legality of their entire income and if it's 100% from haram sources, you are not allowed to accept it from them but if it's mixed income with, preferably, atleast half of it being halal, you can take it and keep giving sadaqa as well to purify some of the wealth.
And Allah knows best,
Mufti Umer Farooq Saleem