Very frustrating, eh? Sounds like the the flannel frayed. Sometimes, it just happens. Not a very helpful response, but I've seen it happen and have never known why it did.

Don't let a bad experience keep you from trying again. I've been sewing for 35 years - and I sew A LOT! - and still make mistakes and have fabrics shred/rip now and then. I don't think it was because it was WalMart fabric, as I've had it happen on other fabrics and I don't buy at WalMart.

Please don't let it discourage you. Flannelette frays very easily and will tear along the grain. You have to overcast the seams especially in the crotch. If you clipped the curve and didn't reinforce it, it would rip right where it was clipped.

I have bought flannelette at Walmart and it was better quality than what I bought at my fabric store. The closer the weave --the better the flannelette--no matter where you buy it.

I don't know what stitches there are on your machine so I'll give you a few options.Here's what to do on the next pair.

After they are sewn and before you do the casing for the elastic. Trim the seams to 1/4 inch and overcast them The best overcast stitch is a three step zig zag---or

Run a medium zig zag stitch next to your stitching line, sewing both seam allowances together and trim the excess being careful not to cut the stitching.

If you are trimming the seam to 1/4 inch there is no need to clip the curves.

Experiment with scraps of material and see which stitch you have on your machine that does a good job overcasting. Refer to your manual but experiment too.

Salgal,
Be sure that the elastic is snug enough around the waist that the pj's don't end up around her hips, causing the crotch to hang too low, therefor tearing easily when her legs are spread(from happily jumping around in her new jammies). Also, you can use a stretch stitch on the seams even though it's not a stretchy fabric. It will give the seam a little 'give'. A slightly longer stitch will put less stress on the seam also, with some overcasting to keep the edges from fraying as Oilpainter suggested. One more thing(trust me, I have 6 GK's, LOL), some rib-knit at the leg bottoms also helps keep the pj's up off the floor and from getting caught under the heels. HTH

thanks everyone.
I am thinking of getting new fabric tonight. I may read up on the stitches before I start again.
I really am anxious to try again.
Thanks for all the tips. I'll try to post with new and improved results!

When making jammies I always stretch curved seams a bit as I sew -it allows a little more give on stress areas.