You can say thank you to anyone if you are grateful for something they've done for you. If your mother makes dinner for you, you say thank you. If she gives you a gift on your birthday, you say thank you. If she goes on a trip and brings a souvenir, you say thank you. If she drives you someplace and you weren't old enough to drive yourself or she did you any favor at all, it's a thank you. You could skip the thank you, but it would be polite to thank even those you're very close with when they do you a favor or kindness.