Child woke up with bites on arm and arm swelling slightly, . is this a spider?

Unlikely. : Spiter bites are uncommon. They don't have a reason to bite us unless threatened. Mosquitoes on the other hand feed off of us, thus the bites are much more likely from them. The swelling, if notpainful or progressively worst, is just from local reaction. Give a little bit of Benadryl (diphenhydramine) for now and see ur doctor if fever develops or if swelling painful or worsening over time. Consider fleas too.

Agree: Also consider bedbugs. These are an increasingly common problem. They tend to bite in a line ( commonly referred to as breakfast, lunch, dinner), and there will be new ones in the morning.