For me, I say:

i) Halszkaraptor, Diplocaulus & Beelzebufo for U18

ii) Mononykus for U19

& iii) Diictodon + Peltephilus for U20 (more likely) or post-EA.

Mononykus and Diplocaulus would be my top two choices, though since we already have Tiktaalik, FROGGE and Diplocaulus could be seen as redundant choices for semi aquatics