The correct choice is 'りました' (forming '撮りました' - took photos). The passage describes past completed actions during the park visit: 'I took many photos of flowers and children.' The plain past polite '撮りました' is natural. 'られませんでした' (could not take), 'り始めました' (started taking - usually not used like '写真をたくさん撮り始めました' without context of sudden change), and 'るつもりでした' (intended to but didn't) do not fit the description of successful past actions.