The "missing child" on the milk carton is "Seven" from season 7.
Because of 'Katey Segal''s pregnancy, she is only shown sitting with something covering up her mid-section, or filmed from the waist up from this episode to the season final.
The girls that Al does the environmentalist work with mention that they "will be doing guest voices on Captain Planet." Captain Planet and the Planeteers (1990) was a cartoon that ran for several seasons in the early-mid '90s, dealing with the dangers of pollution and other environmental threats. It was based on an idea by Ted Turner.