Hi, Charles. This might be a blessing for you. It is not safe to use pressure treated wood for picnic table tops. The pressure treating fluid contains an arsenic based solution that is safe enough for most uses but not in food contact. I would use untreated wood and replace it when it starts to rot, which will take many years since the wood will still be open to the air for drying. For what it is worth, 1x lumber warps a lot worse than 2x and you might consider this.
There are some other things that I have noticed over the years. Wood warps worse when it is brought inside, particularly into a heated environment. Therefore, the worst place to buy wood is from a home center that stores wood inside. I have bought 2x lumber from an outside storage yard in the rain, brought it home and left it under a covered porch and used it to build all sorts of things where it was secured on both ends. It did not seem to warp. If I bought wood from a home center with inside storage, first it was hard to find straight wood, and second, if I stored it in the house, it warped further. If you buy wood from a yard with outside storage, leave it outside until you are ready to use it.
So please rethink your kids table. Don't use pressure treated except for the legs in ground contact. Use 2x for everything and leave it outside all the time. I have an adult sized table like that and it is still in great shape after 15 years. I do put a coat of stain on it every 5-7 years.