I live there - moved from St Albans 13 months ago in order to upsize, simply because of the massive difference in property prices, even though they are about 5 miles apart (and same commute into London). We have a 3 bed detached house in Watford with garden, garage, lots of outside storage, that would probably cost at least another £100k more in St Albans. Maybe £150k more.
I see you are 30 with one DD aged 11 months - I am 31 and DD is 2.5, with number 2 on the way, so very similar! I work in London (Westminster area) and commute 3 days a week. DH works in Watford (secondary teacher).
Pros of Watford: great commute if you are going to live outside London. Takes me an hour door to door to Westminster. Great transport links generally - v close to M25, M1, rail links all over the country. On London Overground rail. Metropolitan line even comes out as far as Watford! Although you'd be crazy to commute into central London using it.
Property prices far lower than many other bits of Hertfordshire.
Big hospital, three new, clean council leisure centres, pretty good shopping centre with all the usual big brands, including a John Lewis(the Harlequin). Two state grammar schools, 100% selective (one boys, one girls) and some othe state schools which are semi-selective and get v good results (eg Parmiters). Some good primaries (eg Knutsford, Nascot Wood). Lovely lovely huge park (Cassiobury) with miniture railway, clean lovely big paddling pools, nature reserve, 2 playgrounds with new equipment, lovely cafe etc. Usual amount of baby / toddler groups / activities etc.
For us, another important advantage is being equidistant between my PILs (Oxford) and my mum (Bedford). Unlikely to apply to you though!
Cons: town centre (apart from Harlequin) v uninspiring. Charity shops, bars and nightclubs, cheap homeware shops. Basically no historical interest or interesting buildings. Not much culture going on. Is a cinema and a theatre, but hardly a cultural mecca. Generally not a hugely inspiring as a town, but for us the advantages (particuarly the commute) make up for this, and anyway we spend weekends either in our house, or visiting people, or going to other places!
It's a real case of weighing up what's important to you - I think our friends in St Albans (antenatal classes) think we are slightly bonkers to have moved to Watford, but we couldn't have afforded the house we wanted in St Albans, and it's more important to us to live in the right house for the next 10+ years, rather than a much smaller house in a better town. And the length of the commute really matters to me, so I didn't want to live in, for example, Hitchin - better property prices than St Albans, but longer commute.
We just came to the conclusion that the perfect town with affordable (to us) property prices and a short commute just didn't exist, and ended up here.
Anything else you'd like to know about Watford, just ask!