Invalid L-value expression; Reference expressions cannot end with conversion

I have read posts about this issue being a known issue and I was wondering if anyone knows how to at least work around it. I am trying to use the Find Children activity and place the Output results into a variable of type List but it does not work. I tried other collection types as well with no luck. I saw people saying that they would remove and re-add the variable to make it work, but I have tried everything I can think of and nothing works. Am I missing something?