A last gasp 21-17 victory over the Dragons provided a winning start, but they were beaten 41-15 by the Scarlets at Stradey Park a week later.
The Dragons will be hoping to use home advantage when they take on a Blues South side who, like the Ospreys have won one and lost one of their opening two matches.
Tomorrow evening the Dragons under 18s travel to Llandarcy to face the Ospreys (7.15pm).
The postponed fixtures between the Dragons and Gogledd Cymru at under 16 and under 18 will now be played on October 12 at Rhymney (1.30pm) and Tredegar (2pm) respectively, and not this Sunday (21 September) as previously announced.
Dragons under 16s: M Davies; J Ramsey, R Lloyd, B Hill, R Davies; T Haynes, J Wright; D Morgan, J Williams, D Maguire, J Bartlett, O Roberts, J Sollis (capt), C Dickinson, C Price-Regan
Replacements: R Stephens, S Brown, J Prosser, L Burgess, R Powell, K Griffiths, E Wheaton
Blues South under 16s: C Allen; H Robinson, J Morris, K Driscoll, M Roberts; R Patchell, T O'Brien; C Hole, P Lloyd, M Taylor, I Matthews, B Smith, E Chilcott, L O'Brien, R Tucker
Replacements: S Bennett, R Rowley, J Delf, R Phillips, S Vial, J B Bruziller, J Hurley
Blues North under 16s: C Edwards; O Rees, R Evans, T Pascoe, S Webber, L Williams (capt), D Evans, D Harris, J Dando, T Jones, A Lee, J Sieniawski, N King, J Perkins, W G John
Replacements: J Elley, C Waters, L Young, E Jenkins, L Jones, G Thomas, L Gunter
Dragons under 18s: W Jones; N Williams, M Jolly, J Daniels, L Folley; L Robling, A Jones; R Jones, M Webber, A Yule, R Wilson, T Crandon (capt), M Morgan, G Jones, C Howells
Replacements: L Jones, L Bacon, G Kemp, G Rogers, H Lewis, J Evans, J Merriman, A Norton, T Rusga