My toddler's insect bites leave dark marks on his legs. Does anybody know of an effective lightening topical cream, lotion, or anything?

Anything that can keep your baby's skin moisturized. For dark marks, we use either Sunflower Oil or Wonder Oil by Human Heart Nature. Very effective especially for my baby's occasional garters marks due to cloth diapers. Other moms swear by HHN's Rescue Balm. Photo credits to Human Heart Nature

Everytime your child gets a mosquito bite, quickly get a warm or hot towel to dab on it. Please dont use boiling water! Works for my brother when he was a child to avoid getting the dark patches.

Hi, you may find this article useful: https://sg.theasianparent.com/heal-baby-scars

Aloe Vera and Lemon juice help to lighten dark marks on the skin

Lemon essence helps with lightening the area.