Hello Nemo! I'd say it in Italian: Cari mamma e papà vi ho amati, vi amo e vi amerò sempre! If you prefer a litteral translation it should be: Cari mamma e papà vi amavo ieri, vi amo oggi e vi amerò per sempre! They are both grammatically correct.

Hi Nemo, love is different in Italian. We would never say "ti amo" to a relative or a friend (it would sound extremely disturbing). You would use "amare" only for your girlfriend/boyfriend, a lover or for your wife/husband. We use instead "volere bene", for relatives and friends. So it would be: Cari mamma e papà vi ho voluto bene ieri vi voglio bene oggi e vi vorrò bene sempre (or "per sempre", it is the same)

Cari mamma e papà, Vi ho voluto bene ieri, Vi voglio bene oggi, Vi vorrò bene per sempre. In Italy we don't say often I love you to a relative or a friend, our way to demonstrate love is saying something that in English I could translate wirh "I feel happy because of your presence in my life". It means exactly"I want you good", but in English it doesn't make sense. In Italian "I love you" is used (too) often in a relationship or maybe if you say that you love your family, but not if you talk with one of them. For example you would say "Mamma ti voglio (tanto) bene" if you talk to your mum, but if you talk to a friend you could also say "Amo la mia famiglia".