If you have kids, and money isn't an issue, then don't listen to the naysayers

You can reach regents park within 30mins using the HEX and the Bakerloo. Go for a quick run around, feed the birds etc. Go to the zoo too if you fancy it, or stroll along the canal back to little Venice. Then head back to Paddington once you've got about 2hrs to departure.

As long as you're not too far from Paddington then there's hardly any risk, and you can always jump in a cab if something happened to the trains.