There is an expression of "It's what you do, not what you say" and I have always agreed with this statement, as hek! a husband can say that one minute and beat the sh1t out of you the next .. but not in your case Miss Kitty, sure they love you to bits.
I don't ever remember my parents actually uttering the 3 little words, but never thought about it to be honest .. just knew that what they did for us, they truly loved their two children. My brother has never said these words to me, but know that he does because of the kind things he has done for myself and my family ... so not always important to actually utter it.
I, like Flashy, say it all the time to my children and grandaughter, so much so that on the closing of a telephone call to my son he says "Love you
too Mum, when I hadn't actually got around to saying it in the first place ! Feel sure once you have said it your Nan would reply, "Well, love you too of course".
Like Margaret's suggestion of a card with it written down .. good starter.