behind their back

so i said i'd "pay a friend back" for giving me rides and by "pay them back" i mean give them a thank you in some way (a card, a mug, a gift something). so i got a gift for a friend with small kids and it was a mug with candy since i was taking time away from their family so i gave the family a gift. i'd also given it to them behind their back in order to not have them refuse it. i'm like please accept it. its a thank you gift.