Magic Grandad

 BBC Educational series
–Year: 1993-2009 (2001)
–Year in film: 1901
–Country: UK
–Who in clothing: Tom ~9 ? bathing costume, knickers
–Who in clothing 2: girl, sailor dress, hist clothes
–Available on DVD: no ?
–I own: no
–Clothing occurrence: low ?
–Rating:  3/10
–Rating: ***
–Comment: Kids (Nicholas Hoult) in historical clothes including bathing suits and historical clothes including flat straw hats. Pic from s3e2. Series "Seaside Holiday with Magic Grandad" within series "Watch". Girl in sailor dress (plain white collar) and boy in knickers in ep Promenade. Set 100 years ago in 1901.

I don't know all episodes. 

Some others also are set in the past (90 years ago) including a bathtub scene. Starring
Geoffrey Bayldon.