for the joints - maybe use a rib knit or spandex type knit -

Are you looking for a "tin man" look like from the older Wizard of Oz movie?

Have no idea the cost involved or the design you are thinking but wondering about using that fabric intended for ironing board covers.

a few years ago I helped an engineer (not the easiest of customers!) to become a robot. I used tomatoe cages (he needed 2, a child would need 1). Turned upside down,push down 2 legs to become shoulders and leave 2 legs sticking in air. Wrap the outside with ironing board fabric (the silver stuff). You could cover it with tagboard first to give it a firmer shape. I opened a circle in the face front and covered it with a black mesh. I used the fabric to make sleeves with a strap attaching across back and front under the cage. Then just embellish with bits and bobs.

There is a product called Soft and Stable, a foam product, that I use in bags/totes. Pliable but strong.

For your youngest, you could put something round around her and tie her to you so she can be the plug on your cord!

I love these ideas! Thank you so much, everyone. I’m not one hundred percent sure what I’m planning to do. I’m still thinking about a design. I’m definitely going to keep the tomato cage idea in mind, and it’s interesting to think over the idea of flexible boxy legs and arms. I saw a really shiny, metallic dance fabric at Walmart today, so I’m excited to try getting some of that material for the exterior. The plug-baby idea kind of cracks me up, too. And I’m going to check out those foams to see what they’re made of. I’ll definitely post pictures if I can figure out how to upload them.

I found a 100% polyester foam that I plan to use. Thanks for prompting me to look more into it :-) ...For those of you who use foam, how do you join the sections? Am I just sewing the fabric in place around it to keep it together? Or do I sew or glue the foam itself first?

look up some steampunk images. wild stuff.

I met a woman at Joann's the other day. She bought some of this to make cooler bags. It might work for your robot project.

https://warmcompany.com/products/insulshine-198