"It's been a few months since they've seen her. They made the decision not to go to her wedding," he said, adding that they do still love their mother.
However, Federline alleges Spears' behaviour on Instagram over the past year, especially her nude selfies, has been "tough" for her sons to cope with.
"I try to explain to them, 'Look, maybe that's just another way she tries to express herself.' But that doesn't take away from the fact of what it does to them. It's tough."
Federline also spoke about Spears' controversial 13-year conservatorship, saying he believes the arrangement "saved" her. He added the situation was hard on him and his children, too.
"This whole thing has been hard to watch, harder to live through, harder to watch my boys go through than anything else. It's been tough. It's the most challenging thing I've ever had to do in my life."
But Federline said he hopes the drama that has engulfed Spears and her family will eventually be behind them all.
"I wish for them to forgive, to reach inner peace and then peace with each other. One day."
Federline and Spears first met in early 2004 and were wed later that year. The relationship ended two years later, shortly after the birth of Jayden.
Federline and his current wife of nine years, Victoria, now live with their blended family of six children.
