Favorite places for toddlers - London/Bath/Cotswolds/Wales

St. James Park in London has a nice playground area that my grandchildren loved when they were ages 2 and 4. Plus the lake in the park attracts lots of waterfowl that they enjoyed seeing.

They also had fun in the wading pool in the courtyard of the Victoria and Albert Museum (see photo below), although it may not have re-opened since the pandemic.

https://www.loc.gov/resource/vrg.12952/

Sounds like you are trying to cover too much territory in the time available. If you are going to Merthyr, it will take about an 1 hour 10 minutes to get from Bath to Cardiff and then another hour to get from Cardiff to Merthyr. Then you have to do the whole thing again in the return direction. It might be better for you to stay at least 1 night in Cardiff - preferably 2. Cardiff Castle is well worth seeing as is the Museum of Welsh Life at St.Fagans Castle - a 25 local bus (Cardiff Bus 32) to the west of the city. The massive medieval fortress of Caerphilly Castle is a 20 minute local train ride north of Cardiff. Castell Coch is another castle just N of Cardiff.

The Brecon Mountain Railway starts at Pant on the north side of Merthyr and takes you into the Brecon Beacons National Park - loads of sheep! https://www.bmr.wales
For the BBNP - a car is best for getting about. https://www.beacons-npa.gov.uk

So, doing a day trip from Bath to Merthyr means you miss out on a lot in that part of Wales. Merthyr itself is a rather miserable place in the former coal mining area - though I can understand hubby's desire to see where ancestors came from.
https://www.cardiffcastle.com
https://www.visitwales.com/attraction/castle/caerphilly-castle-cadw-1891933
https://museum.wales/stfagans/buildings/castle/
https://www.visitwales.com/attraction/castle/castell-coch-cadw-516101

This is a good site for telling you how to get from a to b BUT best to use the train sites for the trains.

Princess Diana Memorial Playground in Kensington Gardens, Mudchute Farm, Hamleys Toy Store, Horniman Museum.

Afternoon tea:https://globetotting.com/kids-afternoon-tea-london/

Why do you assume all pubs are chains?
Try The Queen’s Head.

Take them to ride a double decker bus. Sit up top.

London Zoo is well done. So is the Aquarium.

Take them to walk around and dine in Paddington or Victoria Train Stations

All sorts of street markets to choose from.

Ride the gondolas by the O2.

Walk in Richmond Park looking for the fallow deer.

Cotswold Farm Park is great for toddlers.

Tate Modern is the most child friendly art gallery and there are always street entertainers outside. My kids love the bubble man.

Science & Nat history museums are always really, really busy. The Maritime Museum at Greenwich has play activities for toddlers and you can take the boat there. It’s a lot less crazy.

Victoria Park in Bath has an enormous children’s playground. I nagged to go there frequently.

Just before the pandemic, we spent most of a day catching up with friends who live in London and their 2-year old son, basing our activities on what the 2-year old would enjoy. We had brunch at Giraffe behind the Royal Festival Hall...it IS a chain, however, with three locations in London. Our friends apologized for suggesting it but said they found it to be incredibly child friendly. The food was fine for brunch. We then strolled along the South Bank enjoying street performers, the bubble blowers being a big hit. We crossed the Millennium Bridge and headed up to St. Paul's where we hopped on a bus back to Trafalgar Square, managing to get the front seats up top, which never fails to delight. It was a simple day that seemed to entertain the 2-year old as well as adults.

Another yup for Cotswold Farm Park.

Thank you all so much for these helpful tips!

We took our son on his first international trip to London, York, and Lancashire back in May of 2018 when he was 15 months old. I think London is a great spot for toddlers!

Things he liked:
- Natural History Museum
- riding the double-decker bus
- climbing up the spiral stairs at the British Museum
- Princess Di Memorial Playground and Princess Di Fountains (both in Hyde Park)
- boat ride down the Thames
- being carried through the Notting Hill market
- Trafalgar Square
- Victoria sponge cake
- renting a lawn chair at the Italian Gardens in Hyde Park

Things he tolerated:
- V&A Museum
- Tower of London
- Borough Market
- "Treasures Room" at the British Library
- Serpentine Gallery (free art museum with temporary exhibits, in Hyde Park)

Things he did not like:
- riding the Tube (too noisy, I guess?)
- exhibit rooms in the British Museum (too hot and crowded)
- being inside for more than 2 hours

Also, be aware that using the Tube with a stroller can be very difficult. Maybe it's gotten better, but when we were there, it was such a pain that we barely used our strolled at all. Elevators were difficult to find and frequently out of order. I felt it was much easier to baby-wear and take the bus. We only have one kiddo, so you might find it easier/necessary to have a stroller - just give yourself lots of extra travel time if you're taking the Tube.

Have a great trip!

Erin E brings up a good point. London buses are better than the Tube when traveling with a toddler, with or without a stroller. Less noise, no stairs, nice views on the route. We routinely use the bus rather than the Tube in London ( I hate traveling underground like a mole).

Here is a map of the central London bus routes, and the tourist sites they serve:

https://content.tfl.gov.uk/bus-route-maps/key-bus-routes-in-central-london.pdf

London buses all have level access and space for pushchairs. Wheelchair users get priority for these spaces but I think there’s room for 2 wheelchairs or 3 pushchairs so it is not usually a problem. Young children do prefer the bus. You can almost always get a seat and see what’s going on around.