I would love to take the high road on this one, but your mom sounds like my mom and my mother in law. What I found puts a halt to the comments real quick is a friendly return of the exact same kind of comment right in that moment, only in response to when they do it. At first I was reluctant, because I don't want surrounding people to be uncomfortable (their husbands), but it's so insulting sometimes, I decided to just keep it extremely fair so no one could blame me.
For instance, once I was sitting at a large family dinner, eating and chatting, and my mom said, "A., your hair looks really terrible! You shouldn't wear it like that." (since joining a fundamentalist Amish dressing type community, my mom thinks all females need to wear their hair "swept back in buns" and mine was "down"). I mean,really??! I was 35 years old when she said that, and it was the tenth thing like that in one day. My mom's a great lady, but somehow doesn't understand basic manners when it comes to making judgments. So I just chirped up all friendly in a tone like, "Oh, well if we're doing hair critiques, you could shed 30 years with a bit of color and a flattering cut." Now I didn't want to disrespect an elder or anything, so I said it with a smile like I was joking and a few people chuckled and even she sort of chuckled because of course she's never losing the 4 foot long grey hair in a bun, but it definitely emphasized that the hair comment was out of line.
My MIL has the habit of criticizing everyone's appearance that she sees too, and I don't want it rubbing off on the kids, so when she says, "Oh that lady's hair looks terrible (yes-different hair fixation) I'll turn to my daughter and say-in a friendly teaching tone, "Remember, it's not nice to say mean things about hair just because grandma does it, I never want to hear you do it." so MIL can hear loud and clear. The best is when my daughter says, "I know mom, I think the lady is pretty!" Same thing when hubs swears, I just let the kids know they can't do it, so I put MIL in a similar light and take my "teaching" role seriously. I figure the kids learn how to speak up and defend themselves and others this way, and I really don't care what the perpetrators think.
Stand up for yourself with a "Thanks, but I feed them all day every day, we've got it covered." and a friendly smiling "Really? You think it's OK to say that to me?" here and there. People who take pot shots rarely get resistance. Serve some up! We have the issue of visiting people with unhealthy processed food in their cupboards so I always bring our own hippie stash. They had to get used to it long ago. When they would grumble, I would say, "Hey, as long as I'm the meanie in charge, they have to eat what I say!" I would never have said anything if they didn't start it though, and I do let them slack a little on the junk for visits, but the minute someone is rude to me, I stand up, because I don't want my daughter to go through her 20s feeling shy and bossed around by bosses etc like I did. No one taught me I was just as able to assert myself as these kooks, but now that I know it-life is way better. Your husband will love to see you stick up for yourself, keep your cool, and not get rattled.
Oh, and as for picky eating, we enforce eating to a point at HOME, but like your kids and my kids, many kids are pickier out at strange places and on vacation we like to let it slide and give them whatever. bottom line-none of those biddies business!!