This is a popular discussion....
I personally charge for ALL guests, whether infant or teenager. I don't have that many travelers with absolute infants (as in under one year) so I'm a bit more open to discussion about a real infant but then what if it's triplets under 1 year? Slippery slope. To me, I would charge MORE for toddlers or kids under 6 if I could. In my opinion, families with guests always result in more wear/tear. Food is consumed everywhere, cereal bits ground into the carpet, pen and crayon marks everywhere, dirty diapers left in trash bins, kids running and jumping causing neighbors to tear their hair out, banging of strollers around corners chipping off paint, etc etc. Besides which, kids bathe, use linens, want the apartment warm/cool depending on season, so resources are used. Even with super attentive parents, kids are out of their normal environment and in a stressed situation. Parents as well are either in 'holiday mode' and letting kids go wilder then they normally would allow, or letting kids run around more to wear them out so they sleep.