Sounds like your LO is ready Mine were about 5 months and could sit upright without too many spills when I started getting regular trolleys instead of the ones with capsules (are they made for small babies or what?! My two couldn't fit in the capsule past about 3 months of age, they were too big!). I used to keep a 100cm-2 blanket in the car to line the trolley seat for the girls, but I have seen the proper covers at the local baby store so you could always try there if you're after one