Rott's right. Make some plans for you and the kids and let her know that she's welcome to come IF she wouldn't prefer the few hours to herself....that way you're offering her some 'kid free' time AND giving her the option of 'family' time as well...you allow the choice to participate, HERS to make and YOU become the 'good guy'!
Do something fun that'll keep the kids busy for several hours and maybe even poop them out a little so they go to bed on time T2