Crossword Puzzle It might fill a kiddie pool

Clue: It might fill a kiddie pool

Item missing in this puzzle's theme that's absent as well in the fill and clues (FIFTEENTHLETTER with 15 letters)
Kiddie pool accessories (KICKBOARDS with 10 letters)
Adult in the kiddie pool, perhaps (WADER with 5 letters)
Adventurous airplane of kiddie lit (ARTIE with 5 letters)
Pool addict (BATHER with 6 letters)
Fill-in-the-amount document (BLANKCHECK with 10 letters)
Ashtray fill (BUTTS with 5 letters)
Pool adjunct (e.g. CABANA with 6 letters)
Pool amenity (CABANA with 6 letters)
Kiddie gun ammo (CAP with 3 letters)