PARALLELISM IN A SERIES
When you use a number of phrases in a series separated by commas or conjunctions they must all have the same grammatical form. "They loved mountain-climbing, to gather wild mushrooms, and first aid practice" should be corrected to something like this: "They loved to climb mountains, gather wild mushrooms, and practice first aid" (all three verbs are dependent on that initial "to"). Fear of being repetitious often leads writers into awkward inconsistencies when creating such series.
List of errors