I did this for a friend's daughter's christening last summer, same sort of set up as yours sounds.
Poached a whole salmon the day before at home, served it on a large platter, watercress and pea shoots round the edges, very thinly sliced (peeled) cucumber half moons along it (as scales) and sealed with a thin aspic glaze, made with the poaching liquor. I made a dill mayo to accompany, loosened with a but of creme fraiche, 'twas delicious.
Also did a new potato salad with a cider vinegar and mint dressing, tomato, basil and mozzarella salad with pesto dressing, and a simple cucumber salad with coriander, chilli and mint dressing.
For the children I did a mountain of mini sausages cooked in a honey and mustard mix, chicken satay skewers and satay dip, baked new potatoes with a creme fraiche, spring onion and chive dip and tortilla chips with tomato salsa and guacamole.
All of this can be prepped 1-3 days in advance, with only the chicken satay skewers and sausages needing cooking on the day.
I commandeered a couple of friend's fridges, which helped and, because I'd done it all in advance, stress on the day was negligible.
For pud I'd made the christening cake too, but also made an enormous tiramisu and the children made their own sundaes, helping themselves to sprinkles and fruit compotes etc.