It's not a long walk from the train station to the Lammas Park. You don't need to take a bus. I would say maybe 7 to 10 minutes depending on how fast you walk.
Easiest route is not to walk towards the road but follow the public footpath that is signposted near the (old) footbridge towards the Elmsleigh Centre / High Street. I will post a series of photos in a gallery to help with directions!
If you're coming from London you need to cross over the footbridge and turn immediately left. If you're coming in from Reading or Windsor, come out of the main entrance and again turn immediately left and keep walking straight. There's a leafy pathway that takes you past a couple of houses on your right and the back of the police station, and exits into a car park. Follow across the zebra crossings to exit the car park and go into BHS, opposite. Follow the pedestrian traffic to the front of the store and exit to see Mothercare in front of you. Turn left towards the centre of the Elmsleigh Centre and turn right at Clinton Cards.
Walk to the exit of the Centre and you're in the pedestrianised High Street. Turn left again and keep walking until you see Debenhams on your left.
Here you will see a main road in front of you, but the path runs round to the right past The George. Follow this. In front of you is the Momo Cafe. Follow this road - Church Street - down to the end. You'll go past the Refesh Cafe on your right and at the end is a pub called Two Rivers.
At the end is another road which you need to cross and keep going down Church Street. You'll see the church at the end and a pub called The Bells on your left. Follow the road round to the left. At the point where it meets the river is the entrance to the Lammas in front of you. There's a bridge over to an island in the river and a big barge, but you follow the path towards the band stand and the rest of the park is ahead of you.
Hopefully this doesn't sound too complicated. Like I said, I'll post a series of photos to help.
Thank you so much for the detailed response Siobhan, I had been on Google maps to find a route but was not sure how 'dodgy' or isolated the rail path looked from the map not knowing the area at all and figured that with 2 small girls that public transport might be the way to go. I will look for the pics and try.
I had not realised how spoiled I am having tfl to give buses and transport links/routes and wasted an hour or so trying to make sense of Staines bus info or lack of!
No worries. I will quickly post that gallery to help with some visual hints of where to go.
Yes, I've looked up bus routes before locally and it's not at all easy to make sense of. Easier if you live there and the names of local roads mean something, but not so much if you've no picture in your mind of where they're talking about!