Boyfriend's kids have been really nice to me the last week?

I've posted a few questions on here about this. I'm 28 gay and witha 43 year old bi man. His wife died several years ago, and they had two sons, now 19 and 15. We've been only dating a few months, and up until this week, they've both been very stand-offish to me, and rude. However, this week, they've been really nice. I'm not quite sure why the sudden turnaround. Do you think they're just trying to play mind games with me, or do you think they're being sincere? I don't want to sound cynical, but I guess I am.