I was in the same situation 15y ago. Fortunately the dc all grew out of it by about 6-7.
For biscuits we often had Bourbon Creams, Party Rings, Jacobs Fig Rolls, Garibaldis.
Ice cream: loads available now, but Swedish Glace is really nice.
If you bake cakes, mayonnaise is a great substitute for butter, especially in chocolate cake. My dc like it in any cake, but I prefer it in cakes with stronger flavours. The full-fat Helmans Mayo is dairy free. For all-in-one cakes you can substitute vegetable oil for butter. But as butter is only 80% fat, and oil is 100% fat, you need to do s bit of maths and use only 4/5 The weight of butter. Mayo is a straight sub, no maths. I prefer the taste of Victoria Sponge cooked with oil, rather than mayo.
Sacla Aubergine Pesto is lovely. Nothing like pesto, though! Great just tossed into pasta, with a few halved cherry toms, pine seeds and some fresh basil. Also good added to meat sauces.
For drinks and cereals we liked Lidl's oat milk and most makes of unsweetened almond milk. Oat milk has a similar mouthfeel to dairy milk. I've never gone back to milk, myself.
Sardines with the bones in are the best non-dairy source of calcium.
If you're looking for the savouriness of cheese, umami seasoning and nutritional yeast added to white sauce (made with non-dairy milk, of course) make quite a reasonable facsimile of a cheese sauce.