Wanfang Community Pool is an outdoor pool with sun cover. It has a kid's pool but parents will need to get in with little ones as it is not a paddling pool. There is a very wide slide into the water that is open at limited times during the day. You need swimming caps and swimsuits (not beach shorts). They sell drinks and Chinese snacks like instant noodles, but best to bring your own snacks. You can buy some swim toys if you need them. There is a 7-11 just up the road from the pool. The showers are pretty basic, just be prepared for that. The pool area itself is quite good for families.
Address in Chinese:
萬和街2號(萬芳公園內) Wan-he Street No. 2 (Part of Wanfang Park), Muzha
You can take the MRT (zoo line) to Wanfang Community stop. Come out of the exit. Face the hill in front of you. That road is Wan-he Street. It's maybe a five-minute walk up the hill, less if you don't have kids with you. The pool is on the right, part way up the windy road.
Cost is low, about 50twd for kids and 100tw for adults.
It's fairly easy to find on-street parking near the pool.