Britney Spears is reportedly set to keep paying child support for her youngest son even though he has turned 18. The ‘Toxic’ singer has boys Jayden James – who hit the milestone on Thursday (12,09.24) – and Sean Preston, also 18 – with her ex Kevin Federline, 46, and sources say the performer is going to keep supporting Jayden even though she has the legal right not to continue payments for his upkeep. Sources told TMZ Britney and her former backup dancer ex agreed in their divorce settlement her child support payments for Jayden would stop when he turned 18 or when he graduated from high scho…