Is the waiting period (iddah) incumbent upon the wife if a lawful seclusion takes place between the spouses after the marriage contract, but consummation does not occur therein, and a divorce takes place the following day?

If you were alone with your wife in a seclusion where intercourse was possible, then the iddah (waiting period) becomes obligatory upon her, and she is entitled to the full mahr (bridal-money). The presence of a sleeping child does not negate the seclusion; rather, seclusion is negated by the presence of a discerning person.