Here is the full list of all 9 SingStar Junior trophies - there are 5 bronze, 2 silver and 2 gold.
Sing your first song
Score over 3000 on 5 different songs on any difficulty
Score over 5000 on 5 different songs on any difficulty
Score over 7500 on 5 different songs on any difficulty
Sing 20 songs
Sing 50 songs
Sing 100 songs
Play SingStar® on Christmas Day
Complete a song using the camera feed option