I don't recommend Tea -- I thought the same for my really skinny 3t boy and he was too skinny and the pants fell down. Unwearable
We've had luck with Jacadi. Expensive but runs *really* slim. They have buttons, etc, but my son is so skinny he just leaves them fastened, pulls down and then back up. Adjustible waistbands too, which are of course essential. Available online, although I suggest trying a discount site like Gilt if you can where they come half price.
Other than that, I've found that any pants with adjustible waistbands can work if they are adjusted enough. And just ignore the snaps, etc. With an elastic waistband if you leave those fastened, they can be pulled down, then pulled back up and they will stay due to the elastic.