When your character becomes an adult, look for their favourite meal, snack, clothing, accessory or toy. Collect three of their favourite items and the fourth one automatically arrives 48 hours after becoming an adult.
When your tama is an adult use the item listed under the tamas name in this link https://tama-zone.com/index.php?showtopic=25958&hl= that will take care of the first three the last one comes from having it for 48 hours