Oh, you just visited my house, didn't you? ;)
I've written about this a lot on my blog. Yes, it's perfectly normal for kids to get a bit regressive around this big transition. It would annoy me more if I hadn't seen many versions of this as a nanny already. Usually, I try to do the 'I need assistance' stuff earlier than necessary, so I can break off what I am doing if need be.
Here's a example: three weeks ago, we had a capable little guy who would eat dinner, go tidy up his room, get his pajamas on--- easy as pie. Now, we have the sad-mouthed "I can'ts" creeping out of that room. After some reflection, Joe and I decided to switch the routine so that Kiddo has to get those same tasks (minus pjs, depending on the meal) done BEFORE he even comes to the table for dinner. If he needs 'company' while dressing, I have him bring his clothes out to us and just dress in the kitchen while I put the finishing touches on dinner. This way, the major conflict is knocked out way before bedtime rolls around.
I try to steer clear of language which tells him to be/labels him as "Big boy". He really doesn't want to be big all the time, sometimes he wants to go back to being a preschooler. We try to give empathy when he brings up those conversations, and also keep up our usual expectations as much as possible. Sometimes, a hard hour cues me in to his need for connection. He's wanted to be in my lap *all the time* lately, so we've upped the snuggle time during the day, and also tried not to over-schedule our life so that there's plenty of time to take things slower. (Granted, we are in the position to do that, some families aren't.)
Lastly, try doing some 'alternate' helping: "You go brush your teeth and then I'll help you with X"...give them the opportunity to get help with some things which are convenient for you to help with while assigning them something to do first. Doesn't always work, but it's a bit of a carrot. I do have a couple sticks up my sleeve for not-listening/arguing/not following directions, but that's another post and those sticks only come out when I feel like things are getting really out of balance.
Good luck!