At Narberth, where the Scarlets have an impressive record at all age groups, the Dragons are the visitors, whilst at Llandarcy, the Ospreys take on Blues South.
The Scarlets, who have two victories in three games and 101 points so far this season, will hope to use home advantage to see off a Dragons side who have yet to register a victory this season.
Curtis Morris and Gethin Hunter lead the try tally for the Scarlets so far this season, with three, and both line up in a side that includes lock Jim Gardiner who bagged tries in the victory over North Wales and the 34-19 defeat at the Blues North.
two tries to his name so far this term.
The Dragons were unlucky to go down to the Ospreys in their opening game last month, but were comfortably second best against Blues South at Pandy Park in their only other game.
Down the road at Llandarcy, the Ospreys meet a Blues South side whose only defeat came at the hands of the table-topping Blues North.
On Wednesday, the Scarlets meet the Dragons at Stradey Park - this game has been switched from Llandovery - whilst the Ospreys and Blues come face to face at Llandarcy.
Scarlets u-16: L Treharne; G Hunter, L Harvatt, R James, P Rushesha; J Williams, K Richards; N Bowen, S O'Leary, S Lee, D Colman, J Gardiner, C Morris, O Powell, R Bloomfield. Replacements: G Thomas, A Williams, C Evans, D Evans, R Evans, D Jenkins, G Rees
Tuesday 7.15pm (Under 16)
Scarlets v Dragons (Narberth)
Ospreys v Blues South (Llandarcy)
Wednesday 7.15 (Under 18)
Scarlets v Dragons (Llanelli)
Ospreys v Blues (Llandarcy)