Camp with our three (now 3,5,8) since they were 1,4,6.
We use a camp bed with a folded fleece blanket as a "bottom sheet"; then a sleeping bag; then another blanket. Cold comes up from the ground so it's good to be elevated. You can also store clothes etc under camp beds - we use blue IKEA bags as individual wardrobes.
Everyone wears fleece pyjamas/onesie and thick socks (eg welly socks). So that's toddler, older children and adults.
Sod fashion and style! It gets fiercely cold as soon as it gets dark. Don't wait to change.
April in a normal lightweight tent will be much colder than a yurt etc. Might decide to wear a woolly hat if there's a particularly cold night. At twenty months your toddler will be capable of pushing off a hat or unwanted blanket without waking up, but will whinge and whine if cold.
Potty in the porch to avoid overnight and early morning toilet visits. Line with a (disposable) nappy.
Glow sticks and LED tea lights make great fun nightlights.
Wellies and Crocs are great for getting round the campsite without drenching shoes.
Comics with crappy toys on the front get a lot of mileage.
They'll wake when it's light, so put their beds in the right end of the tent to get the sun last. 
Don't worry too much about brilliant diets. Simple works well. Eg microwave rice pouches stirred through chilli you made at home and froze (defrosts safely in the cool box en route). Fish and chips from the van one night. We have brioche type stuff for breakfast most days with bacon sandwiches if we aren't cooking again. Lunch is bread/ham/cheese/hummus/tomatoes etc that keep well in our powered cool box.
We always take homemade cake with us. We have a layered cake box so can have a few layers of cake that lasts (eg ginger cake, flapjack) and a layer of biscuits. You use a lot of calories camping.
I'll think of more.