I once saw something that said, "Treat getting supplements into your child as if you were giving them life-saving medicine; because you are".
The absolutely huge, life-changing (for us as well as him) differences we have seen once we've got the right supplement in place is astonishing.
And in the reverse case, our lives have simply been shredded by him not getting what he needed for periods. In fact, that's how we ended up where we are at the moment regarding insisting he takes them first thing. But I'm getting ahead of myself.
There's a ton of advice out there on getting supplements into kids but there is certainly not one size fits all. Try things like, applesauce, orange juice, syringing into the cheek and a reward in return for taking them.
None of that worked here.
The obvious thing is to hide the supplements in food but the problem is that some of the supplements taste awful and a few are vile. So eventually you'll either make them dislike food in general (the last thing anyone needs!), make them a far pickier eater, or put them off a certain food forever. Our son makes his "disgusting!" spitting noise if he even sees a smoothie, many years after I tried hiding Lauricidin in one (he'd loved them for over a year previously).
Note, I now sincerely wish we'd started out by getting him to take capsules. Yes, even a low-functioning, non-verbal, defiant child with severe learning difficulties can learn to take capsules. It just takes a while: Taking Capsules Is Doable And It's An Absolute Game Changer!
We do hide some things in food but only things that have no flavour at all (things like MegaIGG2000, L-Citrulline) or very little flavour (like Zinc citrate). But even then we hide very little of things like the Zinc and taste check things to make sure they don't taste too weird. We still hide things because there's simply too much to get in via..
This was very hard but we were left with no choice when he was falling apart (and taking us apart with extreme aggression and continuous lack of sleep). And it now works very well. We are not the only parents to have done this but it's rarely talked about as it seems such a hard thing to do.
We decided that he had to take the nasty tasting but critical powders (opened capsules) first. Before anything else. And, the key point here is: He gets nothing else at all until he takes them.
He quickly understood what the deal was, much to our surprise. We would turn his nose up (quite literally) and walk out of the room at all his favourite treats until he buckled and took the powder. We went through variations of trying to mix it with a treat and at different times of day but we eventually realised it had to be done absolutely first thing in the morning.
We started with them on a spoon and some chocolate (a treat he never gets otherwise) as the obvious reward. But again, never mind the reward, the key point here is nothing else till they are taken.
Easy right?
No. Simple yes, absolutely not easy.
The first day he went literally 24 hours since the last time he'd eaten before he took it. In fact, my wife had to hold him and I had to hold the spoon in front of his mouth before he did. It was extremely emotionally difficult. Extremely. I want to emphasise: We did not withhold food as such, we just made it clear that he could have the food after the powders and would simply walk out of the room. His willpower was astonishing. No, not eating (effectively voluntarily, in my son's case) for 24 hours is not harmful to a child (and possibly helpful!) and if children couldn't do that we simply wouldn't have survived as a species. Endless food supply is a modern phenomenon of the developed world.
The second day buckled at dinner once again, this time making 23 hours since he'd last eaten. And again we held him.
The third day he completely refused again. This time my wife tried piling it on the chocolate and he took it. One tiny bite at a time, but he took it.
The third day he bucked at afternoon snack. We didn't need to hold him this time and he had it on the chocolate.
The fourth day he ate it at lunchtime and the fifth also.
Then he took them at breakfast. With much protesting and crying and attacking me for five minutes. (He had cycled through cute, silly, aggressive and ignoring us over and over again during the previous days).
After about six weeks he generally stopped getting upset for a couple of minutes before taking the pile of nasty powder on the chocolate and he's made huge progress as a result. Really huge. We also started to get our lives back instead of constantly being on guard from aggression and getting three hours sleep night after night.
After two months he started asking for it and is still asking for it after six months!
It has not been easy but as I started by saying "Treat getting supplements into your child as if you were giving them life-saving medicine; because you are".