Honestly, as rare as I need pants. . .

So, VW, you usually wear kilts?

What's wrong with kilts? :p

My sons have been known to wear their kilts to dress-up events! They love to embrace their Scottish side!!

I rip the crotch seam out in the area where you need to put your hand , then zig zag around the opening.  Usually start 1-2" below  the back waistband.  I too use velcro to attach the legs, and if the legs are off, so are the pants.

Build a bear clothing can get expensive. Resale shops and dollar stores work. Garage sales are usually even cheaper.

for cloth of the puppet I am making I use clothes that are to small for my son. Dutch sizes it is 92 (kid of 92 cm long). I enlarged the pattern by 125%I believe that is 18 month til 24 month
For build the bear bears here in our home I use baby size 56 (new born) 62 (1-3 month)
If you have allready clothes of build the bear you can easenly make patterns of the clothes. The basic pattern is always the same the use different fabrics. I do that here too because all the shops in Netherlands and Belgium are closed.
I can make pictures of patterns I have made all ready ,my scanner doesn't work.