What's the best way to get from Heathrow Airport to the Waterloo station area of London: coach bus to Victoria and taxi, local bus to Feltham and national rail train, or other?

I'm thinking the Heathrow Express is the most expensive option possible -- 16+ gbp per person for the train, another 25 quid for the taxi ride to our destination (going on the tube will be the least convenient option -- luggage, toddler, toddler accoutrements).

Thanks.

With lots of luggage plus a toddler, your best option would be a car service such as JustAirports. Many Fodorites here have used them (myself included). Cheaper than a cab, more than the tube; but probably about the same price as HEX but much less hassle.

Book a car from justairports.com
For 3 of you, with that much stuff, it will be the most cost effective and easiest.

Excellent advice. Seems it's less than 40 GBP each way.

Make sure you pay in cash to get the best price from justairports. They charge more for credit cards.