Optimal adherence (>95%) to antiretroviral treatment (ART) remains a challenge among children and adolescents living with HIV (CALHIV). Digital adherence tools (DAT) with reminder cues have proven feasible among adult people living with HIV (PLHIV), with some concerns about the risk of HIV status disclosure. We aimed to assess the needs, contents and acceptability of an SMS-based DAT among CALHIV. We first conducted a survey to understand potential barriers to using DAT among CALHIV, then tested the DAT intervention among purposively selected participants. The DAT intervention included using the Wisepill device, receiving daily reminder SMS and receiving adherence reports on how they had taken medication in the past month. The content of the reminder SMS differed over time from asking if the medication was taken to a more neutral SMS like "take care". Afterwards, we conducted exit interviews, in-depth interviews, and focus-group discussions. We analysed quantitative findings descriptively and used thematic content analysis for qualitative data. We included 142 children and 142 adolescents in the survey, and 20 of each used the intervention. Eighty-five percent (121/142) of surveyed participants indicated they would like to receive reminder SMS. Most of them (97/121-80%) of children and 94/121(78%) of adolescents would prefer to receive daily reminders. Participants who used the DAT mentioned to be happy to use the device. Ninety percent of them had good experience with receiving reminders and agreed that the SMS made them take medication. However, 25% experienced network problems. Participants preferred neutral reminder SMSs that did not mention the word 'medication', but preserved confidentiality. The provided adherence reports inspired participants to improve their adherence. None of the participants experienced unwanted disclosure or stigmatisation due to DAT. However, 5% of adolescents were concerned about being monitored daily. This study showed that DAT is acceptable and provided insight of the needed SMS content for a customized DAT for CALHIV.