You can't. Moreover, you and your kids will be better off when you finally accept who your mother is. While it's wonderful for our children when they have loving and involved grandparents, they can do just fine in life without them. What they need to thrive are devoted parents and a support system made up of extended family and close friends. It's you who's pained by your mother's disinterest, not your kids. They're only negatively impacted if you make it a big deal. They feel hurt because you're hurt.
Expecting our emotionally absent mothers to be emotionally engaged grandmothers is unrealistic and sets us up for disappointment. It's a misguided attempt to re-do our childhoods and try to fix them, turning our detached moms into attentive ones. It won't work, though, because our moms are still the same people they've always been. We owe it to our kids to accept the situation as is, modeling for them that we can't change others, only ourselves. We need to be fully present for their childhoods and not stuck in the past trying to re-do ours.
Michael Singer writes about what he dubs our “inner thorns” in “The Untethered Soul.” When we have an intensely negative reaction, we're experiencing an inner thorn moment (typically, a hurt from childhood). When your mother reacts in a detached way with your kids, it triggers the anguish you felt as a youngster. Yet, if you calmly recognize that and say to yourself “my inner thorn has just been set off, “ you'll stay in control and have peace. Believe me, I do this all the time when my mother visits and it helps me stay sane!