I would recommend not staying in Tumbes city proper, but rather at one of the beach resorts outside of (South of) Tumbes. It's more relaxing and safer than staying in Tumbes city proper.
You can take transportation from your hotel to the Centro Binacional de Atencion Fronteriza (Binational Center for Peru-Ecuador) to enter and exit on the same day. Unless you are adventurous, avoid crossing the border at Aguas Verdes, use the new border crossing instead.
See this link for some background on the new crossing.viewtopic.php?t=24484
Some places to consider just outside of Tumbes in Bocapan (Zorritos) with beautiful beaches and no crowds:
Casa Andina Zorritos -- Four star hotel
Panamericana Norte Km 1232 - Bocapan , Tumbes 24 Zorritos, Peru
Bamboo Lodge 3-star hotel Beach
Km 1223 de Panamericana Norte Zorritos , 24540 Zorritos, Peru
If you really want to stay in Tumbes city proper, the hotel that is considered four star is:
Costa del Sol Wyndham Tumbes (in city center)
If you are able to spend a day or two, we highly recommend seeing the Santuario Nacional de Manglares at "Puerto 25" (this is not the same as the "Puerto Pizarro" tiny version of the Manglares. This is a very beautiful area, please introduce your children to its beauty if you have time! There is also an archeological ruin of interest, called the Cabeza de Vaca site (it is arqueology 'in situ')
If you want info on some reputable guides let us know!