How to talk to parents about their shortcomings?

I'm at the end of my rope with almost 4 year old dcb.

Bit of background:
Dcb incredibly passive and unmotivated. He is also very defiant in a passive way. He will find any way to get out of what he's been asked to do. I have wondered in the past if he may have a cognitive delay, as he doesn't respond to half of the things I say, but after getting to know him - he's been here a year - and performing two separate screens, I've decided it's behaviour instead of ability.

His parents do close to nothing as far as consistency or following through with demands. If anyone recalls my posts about him (numerous) he will tantrum or just flail about when parents pick him up, refusing to get dressed and mom will just shrug it off and carry him out, no shoes or coat sometimes. When I've tried to step in and help he has an all out meltdown.
He's not toilet trained, though he is well aware of when he is about to go (he's held it enough to pee on his pants rather than the potty, and it always hear him pushing when he poops).
This week I've taken away his meals 5 times. 5 out of 9 meals he's finished early because he hasn't listened to my instructions to sit properly, not bounce on his chair, stop playing with his food (and literally pretending his food is a car on the table, making a huge mess).
Today he woke another child up at nap time, just got up and started touching and talking to her (and they have a light up clock that turns color when nap is over, so he was aware that it was still nap time).

So many small issues of defiance, that add up to a lot of time-outs, and I've had enough.

My issue is, it's completely the parents fault. They have no idea how to parent, and as such, have just been 100% permissive with him. How do I explain this to them? Without being overly rude? No one wants to hear "from what I've noticed at pick-up, You are lacking follow through in your commands, this is likely effecting XXXs behaviour" but that's the truth (and now that I write it, pretty compassionate).

I also would like to set a time frame for improvement, but I'm unsure how to phrase it. Is a month enough time to notice improvements in this area?

Thanks in advance... I'm at my wits end!

I tell parents at the interview that we are going to work together as a team through every issue that arises over the years. I also make it clear that I will ask them how they want to handle it but that we MUST both be consistent with our rules so the child learns quickly. If the parents are not doing their part to help the behaviour change they are terminated. It's never that cut and dried of course, termination is never easy, but I deserve to be happy and all of the other deserve to have fun here, not be stressed out little people due to one problem child. It's so unfair to all of us.

So, to answer your question, I tell the parents of an overindulged, misbehaved child to picture them at age 12 and at age 25 and I ask them if they want to raise a manipulative, spoiled adult who will treat other people badly or if they want to do the parenting work while their child is small so they grow into a wonderful adult. Blunt? Yes! But it usually works.

So I agree with luppernoodle, except for the high pitched voice, hehe, I never do that even with the children.

Thanks. I briefly mentioned last night about his behavior and how it's been escalating, but pretty constant over the time he's been here. So she comes this morning telling me that they'll use a timer when he doesn't want to follow a command or count to 5. Also that she will give him a word to describe what he's feeling when he doesn't listen (because I'm supposed to say "you are feeling defiant, aren't you?"??).

I understand basic behavioral techniques, lady, thanks. But there comes a point (and it's before 4 years old) when a child should be able to listen and follow most basic commands, without having to be convinced or talked into it. He actually ends up taking the bulk of my attention at meals and craft time. And he's the second oldest.

I can feel my impatience tingling just reading this. I have a 3 1/2 yrs old who is going through a testing phase right now (he started with me at 2 and I had to work with him then, then he was awesome, and now back to square one) and it's so frustrating. The difference here is that it is a clear result of Mom expecting a new baby and they just found out the sex so there has beena ton of baby talk...he's processing it and acting out in the process. It sounds like it's always been like this for this boy!
It sounds like you are handling it well on your end and yes, the parents need to get on board on their end. Also, the fact that he's not toilet trained is just gross...the only child I've ever known who was not trained at 4 had developmental delays. This might sound harsh but I might be tempted to tell them to take a 2 week break by say, the end of June wherein they work to fully train him. Sounds like there is a lot of laziness on their end.

There is a great deal of laziness. And just overall permissiveness.

I'm trying to decide what to do... I have to give 30 days notice to terminate. I want to give them a chance to work on it, but if I give them 4 weeks, that is basically 2 more months or this.

How much time would you say would give a good chance to see improvement in behaviour?