Currently, I have a reminder on my phone to give them to her and watch her take them, but it’s not sustainable long term.
Ideally the solutions is something that enables her to take the meds on her own.
Of course every kid/situation is different and needs to be met where things are at (and not where you wish it would be), but I think it's worth trying if you have bandwidth. They may surprise you.
When you think about it, most 5 year olds have ready access to very dangerous things; they can turn on the oven, toast things (not necessarily food), they often have access to sharp knives with a minimum of effort, etc. What keeps them safe is their understanding of the risks of those things. The real problem with grandma's pills is that the risk of them is not "accessible" to a child in the way those other things are.
In the long run, I think that a family providing such support should consider adopting some of the best practices of care staff who do medication management for clients. You want a physical log sheet that is formatted like a 2D matrix with recurring doses as row labels and dates written as column labels. The rows should also be sorted and grouped chronologically, i.e. the first row is the first dose to take after waking and it is ordered through to the last dose to take before bed. You typically also want to leave blank space after each dosing period so you can potentially write in new medications when there are changes ordered during the tracking period. You also want to keep a digital copy of the form that you can easily revise and print again as the forms are filled to completion.
The responsible party measures out the doses and marks/initials the cells of the grid for the individual dose and date being administered. In a professional setting, they might mark once for preparing the doses and once again after witnessing that they were consumed. The active log sheet is kept in the same storage area as the medications, readily accessible to the ones administering them. If there are multiple people taking medications, a separate series of sheets is used for each person.
In a professional setting, this supports audit. But in any setting, it also provides a simple process to help minimize dosing mistakes. There are no more questions like, "wait, did they already take this?" after a distraction has interrupted the normal, habitual process. This written formalism can also help you manage refills. Learn to think in terms of "N days' supply" to note on the grid when a bottle is opened, predict when it will be depleted, and mark down when it should be reordered.
Put only one dose at a time in the firesafe so if it's left open, it's empty and no one cares?
I think there are might be some tweaks to make it suit your purpose. But it is worth looking into how it can help senior care as a follow bot.
P.S: I did a ton of research for small farm robotics and met very interesting startup founders in the healthcare/robotics area on the way. If anyone wants to brainstorm or even simply chat about senior healthcare and robotics, please reach out. This is something that is very close to my heart and if I can help make connections even if I can’t help in any technical/material way, it would make me very glad.
I mentioned this idea to my wife and she said it will only make our five year old want them more... maybe we will make a kids version that releases gummies :).
I think we already have a timed version for pet food in the market for portion sizes.