dr jekyll frame in small for sale locally quite cheap, thinking about it as a build up on 26″ wheels for my 10 yr old. can’t seem to find much info or measurements. anyone got any views?

They only come in one size which is a 13″ standard, they released an XL version which I have and is upped to 16″ but will be marked as an XL just behind the seat post on the stays. My nephew rode mine when he was about 11 and it was a tiny bit too big (would help if I knew how tall he was but I don’t sorry) he is what I would say is average size for a kid that age.
It has a very sloping TT so stand over wouldn’t be an issue. I’m 6″2 with a 30 inseam and my 16″ fits so I think if the 13″ frame was a bit too small you would be ok making it fit, likewise with the sloping TT if it were slightly too large stand over still wouldn’t be an issue.

All IMO of course.

eta. Make sure it has the ADS dropouts still on the frame, they are a bit pricey to replace.