Your child has another ear infection, and you need to pick her up from daycare. As you're walking out, you hear others mutter about your leaving. What to do?
Head them off at the pass. If you acknowledge up front that you're inconveniencing someone, it's harder for him or her to resent it. A sincere "I'm sorry" and an offer to take work home shows courtesy and commitment to pulling your weight.
Stay visible. Many moms make up work by logging in hours from home. But if your colleagues can't see you, they may assume you're not really on duty. So if you're working at home while your child recuperates, send regular e-mail or voicemail messages, especially on team projects.
Make it up to them. If someone else stays late to complete a task while you rush to pick up your child, offer her a break the next day. Perhaps she'd like to take a longer lunch while you cover the phones (just clear it with her supervisor).
Keep your boss in the loop. If a particular coworker continually makes comments, it may be time for a manager to step in. As long as you're meeting your commitments, she may be able to communicate your value to your peer in a more palatable way.
Also, if it turns out your coworker really is picking up more slack than she should, your supervisor should know. Perhaps your department isn't adequately staffed and management doesn't know because your overworked colleague has been silent -- at least to the higher-ups.