Kevin Federline says his sons haven’t seen their mom, Britney Spears, in nearly 6 months, and we’ve learned the relationship continues to sour — especially since Britney went after her boys online.

Sources with direct knowledge tell TMZ … Britney’s two boys, 16-year-old Sean Preston and 15-year-old Jayden James, aren’t ready to go see their mom after she blasted their conduct as “hateful” in an Instagram post last month.

We’re told Britney’s post made an already frayed relationship even more strained, and there’s a lot of anger built up against her.

Kevin’s attorney, Mark Vincent Kaplan tells TMZ … “While I will not comment on whether there were or were not regular custodial exchanges, one must consider that the comments about the boys such as those that were recently published hardly create a pro custodial environment. This is something that the parties involved will have to work out over time.”

As we reported, Thursday Britney turned to Instagram to once again post about her boys after 15-year-old Jayden did an interview claiming he felt Britney gave him more attention than Preston. Britney wrote, “”Finally at 40 without the restraints of what my family did to me … I say to my son Jayden that I send all the love in the world to you every day for the rest of my life!!! My love for my children has no boundaries.”

As we told you last month, Kaplan claims the boys feel uncomfortable around their mom, and Kevin posted a series of videos the boys recorded under Britney’s care where she disciplined them.

Remember, Britney’s been beefing with Kevin recently over his tell-all interview that he shot a few months ago with a UK tabloid about their private lives, and the kids are caught up in the drama.

New clips from that interview are set to air Sunday on “60 Minutes: Australia.”