Toddler running indoors U or not?

[Onomatopoeiadoodle]

I live in a flat with downstairs neighbours. They are complaining about my (almost) 2 year old running indoors.

Do you think a toddler running indoors is unreasonable when you live in a flat, if so what can I do about it as we know toddlers lack impulse control and I can't leave him sitting in his play pen all day.

Any suggestions welcome

I cannot get over how many people here expect OP to basically leave her home all day just to suit the neighbours, or expect a 2 year old to not run around and play. Easier said than done to tell her to 'go out more often and for longer'. Living in flats, noise is to be expected. It's not as if she's playing loud music or having parties or screaming matches with friends/partners. Her 2 year old is being a 2 year old in the comfort of his own home.

I think if you live in a flat it's normal you hear your neighbours move around? I would react when it's superloud television or playing the trumpet etc., but a child playing? Then you could also complain of the rain loudly falling on the windows?

Reasonable measures - decent carpeting with underlay(possibly the 2 layers of underlay trick show homes use).
Not running around before 8am after 8pm. Getting out for most of morning to run off energy & I personally wouldn't feel the need to put a toddler in a playpen.
It's reasonable family noise.