Sounds like you may need to put them n a probationary period. Give them 2 or 4 weeks to get their schedule to correspond better with yours. If they have not made the needed changes then he'll need to find care that better suits their schedule.

Sounds like they either need a bit of a reality check to make this work or to move on to something they have more control over. You risk losing them but if you don't make it very clear what you need from them you will not get it.

Sometimes it just isn't a good fit. Seems sad because it sounds like with some simple changes on their end this little guy would be thriving in your care...but the parents need to be on board for that to happen.